As a young man many years ago (ahem!) I read a book about a young boy & girl who explore the ruins of an old church in the centre of Manchester, and then suddenly find themselves transported back in time to the medieval period (I think). Can't remember the name of the book or the author, but "Thursday (or Tuesday?) Street" seems to ring a vague bell... Any ideas, anyone? It probably came out in the 1970s.
It's by Alan Garner. I read a few of his books a long time ago and I remember I really enjoyed them. Can't remember which one is which now, but I think this one may be 'The Weirdstone of Brisingamen'.
Thanks spudqueen, you're a star! It is Alan Garner but it was 'Elidor'. Thursday Street was the location of the ruined church. BTW 'Weirdstone' was set in Alderley Edge. Cheers!