I have a problem which is driving me mad. For the last few months, on a daily basis, usually in the evening, when we turn off the kitchen lights (flourescent tubes), the RCD for the sockets trips, but the lights are unaffected.
Is there an obvious reason for this, as I can't understand why switching the lights off on one circuit, trips the socket one?

Spikes on the supply line can trip cheap RCD's. Read this link and you will see not all RCD's are made equal. There are some really expensive RCD's like this which will auto reset and what we have to decide is how much we are willing to pay? The one in picture costs around £400 and would be used in remote locations where there is no one on site to reset it should it trip due to a spike.

As to cure the first is to select cheap option. I would change the light switch as likely it is arcing a little which is making the spike which in turn is tripping the RCD.