Small and medium-sized business owners have been advised that BT will increase call charges by 10% and its monthly line rental by 50p from the beginning of October.

The majority of customers will be informed of the move by letter this week. The cost of connecting a call will go up from 9.9 pence to 10.9p and the daytime rate rises from 5.9p to 6.4p a minute.

Customers who sign up to a year-long contract upfront will avoid the increased charges.