Is it alright to use English? - in Japanese

My friends and I will be visiting a few places in Japan where we know the staff speak fluent English (Tokyo Disney Resort, a hostel we'll stay in, etc.) I believe that "eigo wa hanase masuka" means "do you speak English?", but we are wondering: what would be a polite way to ask someone if it is alright if we speak English to them, when we already know they can speak the language? Something like "Do you mind if we speak English?"

Side note: in other places, if we ask someone if they speak English and they say no, what would be a polite way of saying "thank you anyway"?

"Eigo-de hanashitemo daijoubu desuka"?
"Eigo-de haanashitemo yoroshii desuka"?

They speak English but don't want to speak? I don't think so. They are happy to talk to you in English definitely.

Thank you, will have to remember those!

You can also say,
"Eigo de hanashite iidesuka?"
which might be easier for you.

Or you can simply say,
"Eigo de gomennasai."
(Sorry for the English.)
and start talking anyway.

As for your second question, I believe you are asking that in case the other party truly does not speak English. In this case, to say "Thanks anyway." you can just say "sumimasen deshita." or just "gomennasai." and move along.

Thank you Uco, I'll make sure to remember those too!