As promised, this article concludes the series on the impact of film and TV on live theatre. Having lauded the benefits two weeks ago, this time around we are looking at some of the negatives.

Top of the list must be the draining of talent. In the past, good playwrights, actors and directors would all have striven to build a career, first on the repertory circuit, gradually ascending to spear-carrying in the West End or at the RSC and then major roles. Only really big stars would have spent much time getting rich in the British film industry or Hollywood. Even then for most, for example in the heyday of Coward, Gielgud and Olivier, theatres would have been a regular haunt.

Nowadays, as soon as any young performer or creative shows a glimpse of promise, they are nabbed (one can almost see kidnapped) by screen producers, often never to be seen again. The more devoted and addicted will make occasional forays back on stage, but these tend to be few, far between and short-lived, given commitments to where the money is. Watch any big budget British movie and almost every actor will be familiar to regular theatregoers from times past, but only a small proportion are now regularly seen on British or any other stages.

This has inevitably changed the way that actors are trained, which is generally not good news for the theatre. Far too few are capable of hitting the back wall of the theatre with carefully honed, powerful voices. Instead, they rely on microphones to amplify mumbling in the hope that it becomes at least barely intelligible. To add insult to injury, we train them in the skills needed to succeed and then film and TV reaps the rewards.

Directors are also heavily influenced by film, frequently turning classic stage plays into mini-(not) movies, which can sometimes seem audacious and exciting but often merely falls between two stools, neither doing any favours to the original script nor working as an enjoyable entertainment for a live audience.

Sometimes, directors and designers also find themselves in thrall to glitzy technology, injudiciously allowing it to get in the way of the acting and storytelling. This might work on screen for Stephen Spielberg but can look incongruous in a small room over a pub.

When it comes to casting, the influence can seem pernicious. At times, one wonders whether it is possible to stage a straight play in the West End without casting stars of stage and screen, regardless of their experience or abilities when it comes to conveying emotion convincingly to several hundred people every night. Indeed, that is what audiences now demand. They would rather see and cheer in the flesh the sexy star on whom they dote than think deeply about the play in which they have been cast.

This leads to the irony that the only way to get a classic on to the stage is to star cast it, with the result that a large chunk of groupies who have paid an exorbitant amount for tickets will not have any idea of what is going on but may not care.

Given the depredations of the economic crisis, when small casts have become necessary to balance the books or restrict the losses, putting film stars on stage also limits opportunities for both budding talents and also experienced stage actors. Even those who do get a look in are likely to be upstaged by the names brought in to sell tickets.

The influence of film, TV and online viewing also has an impact on audience behaviour. Attention spans are growing shorter to the point where many would not consider attending a theatre performance lasting for more than 90 minutes.

Recent news stories about bad behaviour in theatres might also be connected to a change in the demographic, where far too many tickets are sold in the expectation of a drunken night out enjoying a movie-like experience rather than an opportunity to explore serious issues that might change thought, behaviour or on occasion even life.

Readers can decide for themselves whether the overall result is good or bad, but we will have to accept that nothing is likely to change. Even so, to repeat a favourite mantra, theatre has survived for millennia and the latest threat will not kill it either.