question for UK peeps

does anyone remember this show that was on around 1995.....
it was a mini drama on bbc i think, it was shown around 5pm once a week

these 11 year old kids are on a school trip and one kid goes through a portal into another dimension, he meets this girl who he befriends and joins her group etc in fighting these people, during the show he is always trying to get back to his reality and they sometimes wud show clips of wat was happeining on earth with his family and police looking for him.
at the end of the show he finally goes through the portal but the girl jumps through with him so she ends up in our dimension. then it ended.
a second series was never made but the book was released.
it was called something like 'another world' or something and the girl in it kinda looked like a young alicia silverstone.

please help, this is driving me crazy! cast your minds back people!