The convention for writing and displaying geographic numbers (those starting 01 or 02 and related to specific places) is to use a space after the first part of the complete number, known as the national dialling code. For example, 01582 XXXXXX for a Luton number and 020 XXXXXXXX for a London number.
There is no convention for non-geographic numbers, for example, mobile, freephone and special services numbers.
Numbers are often written and displayed with additional gaps to improve clarity or memorability. For example, digits are grouped in pairs, triples or in other combinations. However, the national dialling code should not be split in this way.
Similarly, a space may be used to convey particular information about the number. For example, 0800 800 150 emphasises the 0800 indicating a freephone number.