The law on transplants was consolidated under the Human Tissue Act 2004 which came into force last September.
Under this Act, it is illegal to remove an organ from a live person for reward and to supply an organ for reward. The Act is in fact much wider than this in its scope but essentially makes the removal and sale of transplant organs for reward an offence for which imprisonment can be the penalty.
This means that anyone arranging such a transaction is also committing an offence as it covers the supply of the organ – so not only will you be committing an offence but the person offering to do this for you will be too.
In the and there are strict controls on donation and supply of organs which do not necessarily apply to the rest of the world. If you travel abroad you may have no knowledge, control or reassurance as to the organ you may receive. Equally many other countries ban the sale of organs too so you may well be committing an offence in your chosen country.
You would be better advised to speak to your doctors and look at the websites for the National Kidney Federation and UKtransplant, which is part of the NHS for more information.