The instant service is being run in conjunction with ShareLink and will charge a minimum commission of pounds 20. This compares with a minimum of pounds 20 for NatWest's Touchscreen dealing or pounds 25 for dealing in branches without the service, with pounds 9.95 for postal deals.
Customers at B&W will know the price at which the deal has been struck and can pay by cheque or by transferring funds from a B&W account. Sellers will have to bring their share certificates into the centre.
The centres are in Bristol, Exeter, Edgware, Lewisham and Watford and a sixth is due to open at Ilford, Essex, next month.