“Kick him in the balls and run out of the door.” So advised Joan Collins when asked how to negotiate the infamous “casting couch” – though she admitted that her actual reaction had been to burst into tears.

Rare, it seems, is the aspiring actress who hasn’t been sexually harassed by a director, casting agent or producer, and in recent years many have spoken out about their experiences – from Dame Helen Mirren to Gwyneth Paltrow, Susan Sarandon to Charlize Theron.

The exploitation of actresses – and actors – is not confined to Hollywood. Equity, the UK actors’ union, is receiving ever more complaints and has established a working party to investigate and draw up a set of industry guidelines.

Malcolm Sinclair, the president of Equity, is alarmed that, in their desperation for work in an increasingly competitive industry, actors endure uncomfortable situations and inappropriate questions – everything from intrusive probing about their sex lives to requests to remove their clothes.

“The casting couch has gone on since time immemorial. But, anecdotally, it’s getting worse,” said Sinclair. “Sexual orientation, those sorts of questions – it is becoming extremely difficult. There have even been casting sessions where people have had to show their bodies. This is completely out of order.”

Sinclair is particularly disturbed by the “sexual prurience” around auditions involving young actors. “Youngsters are beginning to feel extremely uncomfortable about questions that are being asked of them.”

Actors are now seeking respect and dignity in the casting process. Nicola Hawkins, an actor-musician, said they are often asked whether they are “comfortable with nudity”.

“Yet when you’re ploughing through the script, you’re thinking, ‘Where is this necessary?’” She recalled a fellow performer’s audition that involved them having “to stand there in their underwear”.

Kelly Burke, an actress on Equity’s women’s committee, argued that actors should not have to accept “degradation and intrusion” as the norm.

The need to confront abuses is overdue. In a 2007 television interview, Helen Mirren lashed out at director Michael Winner for treating her like a piece of meat at a 1964 casting session: “I was mortified and incredibly angry. I thought it was insulting and sexist and I don’t think any actress should be treated like that.”

In a 2010 magazine interview, Gwyneth Paltrow recalled her shock when, at the start of her career, “someone suggested that we finish a meeting in the bedroom”.

Sinclair, who is starring at the Donmar Warehouse with Simon Russell Beale in Temple, the critically-acclaimed new play by Steve Waters, spoke to the Observer as the head of a union that represents 39,000 actors, dancers, singers and other artists. “The complaint I get most is, ‘What are you going to do about casting?’” he said.

Exploitation goes well beyond sexual issues. Actors are frustrated by the increasingly widespread and discriminatory practice of being asked their age. “Ridiculous!” Sinclair said. “How old do you think I am? ‘Playing age’ is a possibility to be asked.”

Earlier this year Coronation Street fired 25-year-old Katie Redford after it was found that she had claimed to be 19 to secure the role of a 14-year-old character. Actress Jean Rogers, a founding member of the National Theatre and former vice-president of Equity, described that as “a very worrying example” of ageist questions repeatedly asked. “The Observer will understand this because it’s done some fantastic work about sexism and a lack of opportunities for women, particularly older women in theatre.

“It’s a particularly sore question to ask an actress how old they are. An acting range was the way the business operated. It’s got worse.”

Ultimately, added Rogers, the profession is about “acting” and an actor does not need to be a murderer to play one.

Burke believes that prying questions – including marital status – “violate” privacy and force actors “into ever-shrinking boxes until all we’ll be playing are the most literal versions of ourselves”.

Actors emphasise that there are plenty of reputable casting directors, but part of the problem lies in that anybody can set themselves up as one, Sinclair said.

The “most disgraceful” exploitation, he believes, affects young actors lured into paying for casting workshops: “They pay £60, £80, £100 – which is a lot if you’re not earning. Whoever’s organising it earns quite a lot of money, [with] no commitment to finding work.”