The prices have been getting better over the last decade or so. Lotus69F2 sold his very nice '72 Twin Cam recently. He asked $34,000, but I don't know what he got for it. IMHO, that would be a VERY good price - maybe the highest I've seen.
Grumblebuns is selling his beautiful JPS for $25,000. He's in California, which should be a good market, so I would expect he could get more if he was so motivated.
Your car looks beautiful! Having Banks do the work will certainly help support any price you might ask. I'm not sure what the market is like in the UK, but if it's like the US, I would guess you could ask between the equivalent of $25,000 to $30,000. If Lotus69F2 got his asking price, you could add at least $5,000 to both sides of that range.