Check you policy booklet. There will be a paragraph defining the Territorial Limits
My policy, from Carol Nash, underwritten by Equity Red Star, certainly covers me for Hungary, Slovenia, Slovakia and Czech Republic. I can't remember which other countries were included.
Also, if you are going for an extended trip check the time limits for overseas trips. They vary a lot. E.g. some companies only cover 1 month, some 90 days. Some cover as many trips as you like in a year but each trip must be less than a month.
Most insurance companies will allow you to extend the territorial limits to visit a particular country, for a fee of course. This applies to the length of trip too.