I've just joined this forum but have been doing the Listener for about a year and benefiting from some helpful posts. Thank you. I enjoy all the puzzles, because they have clearly been set by clever people, provide varied challenges and cover all sorts of themes.
Some of the posts about maths surprise me. There aren't many mathematical puzzles and the maths involved is never more than is taught for GCSE. The puzzle about perfect numbers last month was a brilliant piece of logic. I'm a linguist by the way.
Regarding this puzzle, like Mondo says, it was hard to get going but once I got the last across and down clues, it got easier.
By the way, symmetry is either rotational (like the letter S) or line symmetry (like the letters A or B). This puzzle is both (like the letters X and H), so apart from not wanting to give the game away too much, there was no need to specify the type of symmetry.
I think Greengage is right: the string top left does meet the two parts of the instruction.
Can anyone give me a guide on the string top right? I have the last three letters but my answer for 'big house at Kelso' does not provide a first letter that works.