More about Williamson than O'Toole, but this article asks the same question, i.e. what happened to working class, hell-raising thespians?
http://www.telegraph.co.uk/culture/theatre/9041813/Will-we-ever-see-an gry-young-men-like-Nicol-Williamson-on-the-stage-again.html

Overall a deeply impressive list Edward even if the hell raising dented their potential. Highly unlikely we'll see their like again, particularly if Julie Walters is right:
An even bigger problem is that acting ability as such is increasingly undervalued relative to having the right "famous for being famous" persona. Otherwise Benedict Cumberbatch would be better-known than an acting joke like Keanu Reeves.

Thanks a lot for the kind answer.
"How is it possible to feel nostalgia for a world I never knew?" - The Motorcycle Diaries

This quote has been brought up in several articles about him:
"I'm not from the working class. I come from the criminal classes."
Not sure if he goes in detail about it in the first volume of his autobiographies.
At least two of his obituaries mentioned the part about his childhood friends (the one from the Mirror and the one from The Guardian).

Where did you get this info from? Just curious. A book?
"How is it possible to feel nostalgia for a world I never knew?" - The Motorcycle Diaries

Fun fact: Peter himself denied to come from the working class background, stating that he came from the criminal background instead. Three of his childhood friends were hanged for murder in their early 20's.

I would add Dirk Bogarde
Bogarde came from an "artistic" family, as I recall, very different from the blue collar backgrounds of O'Toole the rest.

Interesting list. I would add Dirk Bogarde although I know nothing of his offscreen antics.
"If you're laughing, I defy you to be afraid"

At the slightly younger end, I suppose Anthony Hopkins could also make the cut.

I think the OP mentioned already the ones who match all the requirements: British, coming from the working class background, hugely admired, hellraisers, having enjoyed a reasonable amount of success on film (Williamson could have done even better things, but he had his great cinematic roles too).
Alan Bates
never had an alcohol problem. His main weakness was being a sweet tooth, which lead him to get diabetes and badly affected his health. The hellraiser label doesn't quite fit him: he was a rather quiet person, although he apparently had a darker side (his biography mentions that he always felt himself guilty for slightly neglecting his children, one of which sadly died of an overdose at a young age).
I don't think
Tom Courtenay
was a hellraiser either. I remember him once stating that one of his most unhealthy habits is to have just a glass of wine with his dinner.
Albert Finney
is often put into the hellraiser club, but there aren't many drinking anecdotes about him as there are about the others. I believe he was less extreme in his habits.
Michael Caine
has never been known for his stage work, but he began as Peter's understudy in the original stage production of "The Long, The Tall, The Short" and there is an story about a lost weekend he spent (or better didn't spend) with him at the time. In his worst period, he used to drink 3 bottles of vodka a day. He also rose to fame with a British kitten sink drama, 'Alfie'.
You might want to add for one reason or another:
Peter Finch (1916-1977)
: Born in London into an intellectual family, was raised in Australia, but soon returned to England and became one of British cinema's top leading men. Also an accomplished stage actor and one of O'Toole's closest friends. There's the legendary anecdote about the two of them drunkenly buying a pub because the owner wanted to close it for the night and have them go, befriending the man once he gave them back their cheques the morning later and eventually crying at his funeral a few years later just to find out that they were in the wrong place. Classic.
Laurence Harvey (1928-1973)
: Born in Lithuania and raised in South-Africa, he eventually relocated to England where he became a top leading man of stage and film. His performance as Joe Lampton in 'Room at the Top'; raised the high bar for all the anti1354-heroes of kitchen sink drama. Heavy drinker and smoker, he was often involved in alcohol-related competitions with Harris in the 50's. He didn't have the universal acclaim as some of his pals back in the day and his relationship with critics was a turbulent one. He still has detractors, but I, for one, am a big fan. He was close to Peter, who paid a touching tribute to him in 'Venus'.
Ian Hendry (1931-1984)
Mainly a TV star, but associated to some noteworthy British movies of the 60's-70's such as 'Children of the Damned' and especially 'Get Carter'. Always considered an actor of enormous raw potential. Destroyed by alcohol. He truly looked scary in his last public appearances.
Robert Stephens (1931-1995)
: I don't know about his family background, but he was another acclaimed stage actor from that generation that was destroyed by his alcohol problems. He never hit it big on film: his biggest personal success was probably 'The Private Life of Sherlock Holmes', Billy Wilder's least memorable movie, as far as I'm concerned. Frankly, I've never been much impressed by his silver screen legacy, but maybe I would feel differently if I had ever seen him treading the boards.
Tom Bell (1933-2006)
: another certified hellraiser. Was successful on the stage, not so much on film. He looked like he was going to be big for a while in the 60's, with 'The L-Shaped Room' being arguably his greatest moment of triumph. But his drunk antics eventually damaged his career.
Peter Wyngarde (b.1928/1933?- depends on your source)
: Don't know if he had any classical training. He had a reputation for being a bad guy and troublemaker in real life and had several legal problems that eventually forced him to give up his career in the early 90's. Most famous for his TV work, his most important film was "The Innocents", where he played Peter Quint.
Dudley Sutton (b.1933)
Started as a young angry man in films such as 'The Leather Boys', but career was set back because of alcohol-related problems. He's mainly been a supporting player for the rest of his career, but at least Ken Russell gave him a great role in 'The Devils'. Interestingly, he's in 'Katherine of Alexandria', Peter's final movie.
David Warner (b.1941)
: Not a hellraiser according to himself. His performance in 'Morgan: A Suitable Case for Medical Treatment' is one of the best portrayals of young angry man in a British film of the 60's. An accomplished Shakespearean. Has tons of garbage in his filmography, but he never encountered the problem of finding himself unemployed, that's for sure.
John Thaw (1942-2002)
: Mainly known for his TV work, although he was in 'The Bofors Gun' early

Grammar School (ie. exam selection but non-fee paying) and RADA Scholarship - described it himself as a
"Middle Middle Class"
upbringing (
http://alanbates.com/abfeatures/bio.html
). A bit posher than I thought, possibly a bit less than you thought, but if the "angry young men"/"kitchen sink drama" movement has any application - his exclusion as
just about
'on the wrong side of the tracks' has merit.
Although a vicar's son a case can be made for including John Hurt in the lineage - another RADA scholarship and a struggle with no 'silver spoon' by any means. Finally, I'd have pressed strongly for Malcolm McDowall too, (working class but boarding school "educated")
if he'd only stopped acting 31 years ago.
Overall a deeply impressive list Edward even if the hell raising dented their potential. Highly unlikely we'll see their like again, particularly if Julie Walters is right:
http://www.telegraph.co.uk/culture/culturenews/9515821/Julie-Walters-w arns-of-future-where-only-posh-can-afford-to-act.html

Good call on the (still living) Tom Courtenay, he certainly belonged on my list of "angry young men" actors.
I was under the impression that Alan Bates came from a more upper-middle class background, which was why I left him off the list.

Alan Bates (died 2003) and Tom Courtenay (born 1937) might press for inclusion - Oliver Reed while bereft of classical training, did hold multiple compensating PhD's in Hellraising.

I thought that Finney was a few years younger than that. I'm glad he's still with us and still appearing in films, regardless.

Albert Finney was born in 1936, along with Nicol Williamson. Harris, 1930, and O'Toole, 1932.
Shaw and Burton
are a decade older than the rest.