I have just finished reading, with great enjoyment, Valerie Grove's new biography A Voyage Round John Mortimer (Viking, £25). Though an authorised account of the writer/barrister's long and eventful life, it is far from toadying in its approach. National Treasure he may be, but Ms Grove does not pretend he sparkles in all areas. One of his faults is - or at any rate was - a propensity for being rude to waiters and the like. This, curiously, is a character flaw he shared with Sir John Betjeman, from whom he inherited the National Treasure title. Perhaps it goes with the job.

Of course, it would have been very difficult for any biographer to present the second Sir John as squeaky clean, since his dirty washing (including his love child with the actress Wendy Craig) had already been aired in Graham Lord's earlier unauthorised biography. (Most reviewers of Grove's volume wrote cuttingly of this book. I suspect not many had read it, because actually it was rather good.) The big story that Lord broke was the fact that not a line of Mortimer's submitted script was used in the hugely successful Granada TV adaptation of Evelyn Waugh's novel Brideshead Revisited. Grove rehearses the facts of the matter but very improperly, I think, tries to make light of it.

The story, in a nutshell, is that the six episodes of Brideshead that Mortimer wrote were a disappointment to its producer Derek Granger and director Michael Lindsay-Hogg. He rewrote them, but even before they were delivered, Granger and Lindsay-Hogg decided not to use them but to work directly from the novel. They were doing this throughout the summer of 1979, when some scenes were shot on location in Oxford. I covered the first day of filming in the University's Botanic Garden and was standing next to the photographer who took the picture above. Later in the year, when filming resumed after a long technicians' strike, the same approach continued under Charles Sturridge, the new director (Lindsay-Hogg had commitments in the US).

On the set on that long-ago August morning, I was fed the line that Mortimer was the scriptwriter, and dutifully repeated it in my article the following day in the Oxford Mail. This lie - for let's not mince words - continued to be told and, of course, with more and more emphasis as Brideshead- mania took off. Mortimer derived great éclat from his association with the series. To be fair, so too did the series from its association with a writer of his eminence. This was a deception that suited both sides. But did it suit a cheated public? I for one was furious to learn, on reading Lord's book, how we had all been duped. At a time when we are much concerned with the deceptions being practised on TV, the story seems astonishing.

Ms Grove reveals that Mortimer was handsomely paid for all 13 hours of the scripts, but she writes: "Consider how awkward it was for him to be on the receiving end of plaudits, in perpetuity, for a work which in stye and substance could have been his, but in fact was not. Whenever Brideshead was discussed, he fell into the habit of purring modestly and murmuring, 'It was Evelyn Waugh's script really'." Maybe he did, but Mortimer certainly traded on the Brideshead 'factor' when it suited him. In all the books of his I possess, however short the author details are, it is always stated that he was the Brideshead scriptwriter.

Someone who certainly deserves all the credit for his writing skills on a TV script is the actor David Haig, who gave us Sunday night's My Boy Jack on ITV. Our television critic Tony Augarde warmly applauds it today on Page 30, and I heartily concur with his judgment. Having twice seen Haig's original stage play, I was intrigued to discover how cleverly it had been opened out for the screen, including splendid scenes with George V and his epileptic son Prince John.

What a contrast this superb drama was with the overblown tosh offered the following night by the overpraised Stephen Poliakoff in Capturing Mary. All style and little substance, this was a waste of the talents of Maggie Smith (who in old age has more wrinkles than Mick Jagger). David Walliams, I thought, was appallingly miscast - far too oikish (those vowels!) to play the schmoozing socialite Greville White, whose revelations about other upper-crust figures were at the centre of the drama (what a pity we didn't learn what they were).

In fact, there was more than a trace of Brideshead about the whole thing. Narrator figure (Charles Ryder/Mary Gilbert) looks back on long-ago visits to grand house, during which he/she discovered how the toffs live. In Greville was a character very like Rex Mottram (with overtones of Scott Fitzgerald's Jay Gatsby and Anthony Powell's Kenneth Widmerpool). The lushness of the camerawork and evocative music invoked comparisons with Brideshead too. The big difference was that Waugh had something to say and Poliakoff didn't.