Alistair Darling has brought a cat to Number 11, it emerged last week, the first cat to roam around Downing Street since Humphrey left amid rumours that Cherie didn't like cats.

But Darling's cat is not there to mark a break with the Blair's, TS has learned. Our man with a hotline to Darling can reveal that the cat is there because it is good at catching mice.

'Sybil has been brought down for an extended stay because there is a mouse problem in Number 11,' Darling said. 'She is a good mouser. I haven't seen a mouse myself but I am told that since Humphrey was retired there has been a problem in Number 10 and Number 11.'