Is it legal to have a light switch in front of copper pipes...

[ban-all-sheds]

Without going to get the Big Book out, I'm pretty sure the relevant regulation specifies a minimum distance of 25mm between mains cables and metallic services (50mm for gas).

It would have been wise to have got it out.

However, given the quite high ambient temperature created by heating pipes,

How high is that?

I would instinctively want to maintain a greater distance than 25mm between those and mains current carrying cable(s). I would also definitely not want them in direct contact with each other!

What temperature does the surface of HW or CH pipes reach?

I'd consider putting coaxial or data cables in the same trunking as heating pipes (no doubt some will shoot me down for that) but not mains voltage cable - possible heat damage and derating factors would render it very unwise, regardless of whether it's heat resistant or not.

So you think that heating pipes could damage even heat resistant cable?

On what grounds?