UK Fitting a timer to an electric aga so it can't be used in the night

[mainline]

A few months ago I fitted a change over switch to an electric oven/hob and a converted to electric aga stove, stopping them being used at the same time.

I've now been asked to fit a timer so that the Aga can't be left on overnight.

I'm not happy to do this for various reasons, but can anyone think of any regs I could quote.

 

[brianmoooore]

They think the supplied one might be too small for their needs, or it's a Wok type thing that they think mightn't be supplied at all (they would be right).
History now, since the one induction hob has been replaced by a conventional one.