Ethics of "Double Dipping": Helping 2 professors with research during the summer Some Context:
Over the past year, I have built relationships with 2 of the professors at my university. In this case, I was referred to Professor X by Professor Y. The professors work in two related fields (physics) and are friends.  

I worked with Professor X on some of my research a few months ago and it went well. Professor X is allowing me to help him with his lab research over the summer and I am honored to do so. Of course, it would not be an every day thing and we will be working out a schedule. 

Consequently, I spoke with Professor Y about a summer spot before starting my research with Professor X. Nothing was formalized here and I haven't spoken to Professor Y since beginning my research. However, I am very interested in helping Professor Y in her lab this summer. 

My Question: Would it be seen as poor taste to ask Professor Y about helping in her lab this summer? In my email I would explain that I would also be working with her colleague. 

I don't want to jeapordize my position or my relationship with either one of them, so, would it be considered "double-dipping" to help with both of them? If it is, would this have any adverse effects?

One option would be to ask Professor X if he would be alright with this. I am not sure about this option because again I don't want to put our relationship on weird terms. 

This is undergraduate level, in the UK.
This shouldn't be a problem. The professors aren't your employers who demand 100% of your time - they might not even be paying you - so they are not likely to expect you to commit to their lab and their lab only (it'd also be unreasonable if they expect this). Meanwhile by working in two labs you're maximizing your exposure, which can only be a good thing for you.

The only serious consequence I can see from this arrangement would be that you might not be able to commit enough time to actually achieve something substantial. If you aren't going to get any real research done in both labs, you might as well commit to one lab only.