Bomber Harris,
The ATCO might have been trying to reassure you - a TCAS RA is still something that is irregular enough that it could cause consternation to the receiving crew.
However, as you state, you still have to follow the RA so the call is pointless and could actually cause confusion or distract you. There is no excuse for it from an ATC (UK) pont of view.
One other point though, again possible mitigation. You have some quite busy airspace in the UK, the ATCOS are, on the whole, very good at what they do. It is their job to be in control and 2 or 3 steps ahead of the game... it's what we pride ourselves in being able to do.
Bearing this in mind, the call 'TCAS RA' can be very disconcerting and confusing to an ATCO who thought they had everything under control.
The reply you mentioned, although it should never happen, might just be the ATCO verbally affirming/assuring themselves as much as it is a call to you...
If you can imagine, the ATCO has several aircraft climbing and descending, but the ones that will come into proximity to each other all have been given levels that maintain 1000' seperation. Then out of the blue one of those aircraft calls a TCAS RA... the ATCO should only acknowledge, no traffic info to be given, but they are only human and they might inadvertantly transmit something they shouldn't have, especially if the traffic situation is fairly complex and they've worked really hard to solve all the conflicts.