BT does not endorse any service for the buying or selling of shares. Stockbroking services are available through brokers and banks. Only registered brokers and banks can deal in the market - everyone else has to deal through them. This way, there is a controlled and regulated market.
When buying or selling shares, you will usually pay a broker's commission each time you buy or sell. Contact your broker for further information.
When you buy shares, you are liable to pay stamp duty (for UK equities this is currently 0.5 per cent of the share price) but not when you sell.
How your shares are held will influence dealing costs - there may be higher costs if you hold a traditional paper certificate.