I thought it was Eric who had the temper & treated Claire poorly. I did think it was strange when the one son sat in the car & then sped off, but figured they were both having trouble dealing with the possibility of their father being a murderer, coming on top of Claire's Alzheimers. I'd have to watch the show online again, to catch further nuances between them. I was amazed after-the-fact, to realize that Eric Slater was played by Tom Courtenay; hot stuff back in the day.
I found this link recapping the show; it includes this excerpt (highlighting is mine):
With Eric’s murder charge in the news, the rest of the Slaters have to deal with the press pack and Claire gets packed off to a country hideout. With her mental deterioration only likely to accelerate, no one thinks a successful prosecution possible. Even though a flashback confirms she remembers murdering Jimmy, how could she reasonably defend herself? Eric will do time in prison but Claire gets away with a supervision order.
Don’t imagine that’s a victory, though. We haven’t seen much of the Slaters’ younger son Mattie (too busy “poncing off back to London”, to quote his brother) but it looks as if Claire is going to be seeing quite a lot of him. “Me again,” he says with a malevolent glint in his eye as he gets her alone. His regular visits to his mother are merely to play Bait the Pensioner, tormenting her with sundry cruel tricks. You can understand the resentment, but he’s getting way too much pleasure from it.
