I wondered that too when I saw how little tax the finance sector is paying.
However, it occurred to me that stamp duty which is payable by the purchaser of shares on transactions whose consideration exceeds £1000, might make a tangible contribution where the purchaser of said shares is a financial institution.
I suppose there might also be a tangible contribution from stamp duty where the purchaser is not a financial institution but the purchaser is nevertheless is engaged in buying substantial amounts of shares (eg in corporate takeovers etc). In such cases, while the finance sector is not of itself contributing to Government receipts, the fact that the business is being conducted through London rather than Frankfurt, say, implies that the receipts would be lost if the business moved away from London.
This is quite interesting, I think. Can anyone point to a source of such information or relay any facts they have?