Firstly Simon, let me say, nice guitar!
They are rare, especially in the UK, and like all mid-60s Gibsons they are quite highly sought after.
So what is it worth... I would suggest around £2500, assuming there are no breaks/replaced parts. Now, that doesn't mean it'll get that particularly easily. In a vintage guitar store in London/New York/LA etc it would most likely be offered for sale at twice that - where it would sit for months/years before eventually selling.
If you stuck it on ebay tomorrow with a start of £1 there is no telling what it would fetch. Anywhere between £1500 and £3000 depending on precise condition, and who wants it and how bad. I'd be disapointed with £1500 and delighted with £3000. Personally, if I were selling i'd hold out for £2000-£2500, and expect it to take a bit of time (based on the condition I think I can see in the images)
There has been one sold on ebay recently in the US which fetched (equivalent of) £3667 (actually $5050), but is in very clean condition - hang tags and all (see here
1966-Gibson-Trini-Lopez-Electric-Guitar)
You would certainly have got more 1 year ago. If you intend to sell, make sure it is available to Europe - a strong Euro is making things like this easy to export to the continent just now.