Will a Japanese 4G ipad work on 4G in UK?

I want to buy a 4G cellular + wifi ipad when I visit Japan next week, but cannot discover whether it will function correctly with a UK 4G card when I return home. I understand ipads are not locked but will Japanese ones accept a UK 4G card? Thank you.

You need to be more specific.
Which Japanese provider's version of the 4G iPad are you talking about?
Which provider's 4G network would you like to use in the UK?
Start by comparing the 4G band (frequencies) used. Find out which 4G bands the iPad you're targeting actually supports.

I think only EE have 4G technology in the UK just now, so it would have to be with them as a provider - I only want to ensure that if I buy an ipad in Japan, the cellular bit will work in UK! I will not be using it in Japan as I live in UK.

You should check prices in the UK, because they may not be cheap here in Japan for an unlocked one.

A new unlocked iPad2 with 32G, WiFi & 4G may cost around 70,000+ yen

forget about buying any new tech in japan, it's cheaper in the UK! Due to the current poor exchange rate it's not worth buying anything in japan that you can get elsewhere.