It's lovely. I can't really help with a valuation as a replica like this has to be worth less than a genuine Cooper S, but one of this standard is such a rarity that it's probably not worth 'that' much less?
All I can really add to the above replies is that IF I had the money I'd happily spend 15k on this, maybe closer to 20k? For insurance, I'd certainly start high with them and work back from there. Maybe I'd even go with the suggestion that it's worth £25k and work from there?