As time wore on and number shortages became more acute, local numbers were gradually converted to five-figure or six-figure numbers, and the STD code changed to the (0xxx) format.
In written form these area codes were split after the third digit to highlight this satellite exchange numbering.
Telephone numbers in the United Kingdom have a structure that reflects their historical demands, starting from many independent companies to a system that supports many different services including cellular phones which were never initially envisaged.
all except the telephone service of Kingston upon Hull and Guernsey had been bought out by the Post Office.
The Post Office also operated telephone services in Jersey until 1923 and the Isle of Man until 1969 when the islands took over responsibility for their own postal and telephone services – although the Isle of Man system remained part of British Telecom until 1987.
Post Office Telecommunications was reorganised in 1980–81 a s British Telecommunications (British Telecom, or BT), and was the first major nationalised industry to be privatised by the Conservative government.
Within the London director area, a number on the Frobisher telephone exchange would be dialled as FRObisher xxxx.