Unfortunately, it doesn't work like that.
Mary Beard is undoubtedly a fine scholar. But the role of historical consultant in these sort of programmes is an advisory one. They are someone that the programme-makers turn to for ideas, but they do not write the scripts, or dictate how the programme should be made. They do not have the final say, and one suspects that they are often overruled. As a for instance, Mark Horton is the archaeological consultant on Bonekickers. Now, he may well have told the creators that anyone using a magnetometer must ensure that they have no metal about their person. He may even have said that this includes underwiring on bras. But I doubt he explicitly endorsed a scene where students are told by a member of staff to remove their bras, making that instruction in front of another, male, member of staff (something that I would expect to lead to a complaint of sexual harassment in any university I've ever been associated with).
The power is with the programme and film-makers. The historians only know how to write books; the directors and producers are (they will argue) the ones who know what will work on the screen. And sometimes they will be right - good history does not always make good drama. Just look at Oliver Stone's Alexander, a film that (in my view) is dramatically weak because it pays too much respect to history. But sometimes decisions seem to me to be symptomatic of a lack of faith in their audience.
Beard's post about her involvement with Ancient Rome is interesting. At a seminar, the producers explained that their prime objective was to prevent people changing channel. A lot of careful research has been done into people's viewing habits, and this is used to shape programmes. So complexity is avoided, for fear that people will change channel to something less taxing. If they want to get more of the story, the idea seems to be, they can always buy the accompanying book (I've certainly had that argument put to me, though not by a programme-maker).
This seems unethical to me. History programmes should not be in the business of falsifying history. It's not enough to say that the true story is in the book - most viewers won't read the book. And the BBC's reputation as a maker of historical documentaries was not built on catering to the lowest common denominator. Programmes like Civilisation assumed an interested, intelligent audience, who might not know the subject being discussed, but didn't need patronizing.
To return to my point about consultants - why do programme-makers make such a play of using consultants, if they will overrule them where necessary? Because consultants lend authority, to give the impression that their programmes are unquestionably historically accurate. This is important to programme-makers - a lack of perceived authenticity will hit their audiences. By hiring Mark Horton, the makers of Bonekickers hope to promote the notion that the show displays an authentic version of life in an archaeology department (which it isn't, of course). The hiring of Mary Beard and others allows the makers of Ancient Rome to back up their opening caption that the programme is dealing with real people and events, based on ancient accounts (as if those weren't problematic), and with the collaboration of modern historians. So what you see is true. Personally, I worry about the pernicious affect of such statements, and the way that the drama-documentary actualizes a particular version as The Way It Happened. Take, for instance, the programme on Tiberius Gracchus. Not only does the version show excise Tiberius' brother Gracchus from the account (too complicated, one presumes), but at the start brings together two pieces of evidence in a way that may not be sustainable. We know that Gracchus was present at the fall of Carthage in 146 BC. We also know that he won acclaim for being the first onto an enemy city's wall in the African campaign. But we don't know what the programme postulates, that the city concerned was Carthage. Indeed, one might suggest that it probably wasn't Carthage, as if it was, our source, Plutarch, might have been expected to tell us. Television drama strips this from the accounts. So, remember, don't consume the packaging. The quality of historical consultant is not necessarily a guide to the historical integrity of a programme.
So why do historians still serve as consultants on these programmes? Obviously, I can't speak for anyone. And I shall put aside the notion of sheer ego-boost from being connected to the telly, though were I ever to be offered such a role (which is highly unlikely) it would be an influential factor for my decision. I think many get involved because they see an opportunity to do some good, at the very least to stop some mistakes being made. Bonekickers has its clearly 'educational' moments, such as the mini-lecture on how Bristol, though built on the profits of the slave trade, never actually had slaves in its ports. And Mark Horton has a series of mini-films on the website on the background. So those interested in learning more about the history can be directed. Maybe that's the right attitude, as long as your ambitions aren't too lofty - in which case you'll be disappointed, as Kathleen Coleman was when she worked on Gladiator. But maybe it's appeasing the enemy? Will Bonekickers have the same effect as Time Team, in encouraging a false view of what life in an archaeology department is like? I'm not sure I know the answer to that one.
Edit (23/07): There's a good article here by Paul Cartledge, talking about his involvement in The Greeks, why he did it, and why he'd do it again (as indeed he did, for The Spartans).