Linked numbering scheme

A Linked Numbering Scheme (LNS) is a numbering plan applied to an area of the country where calling between lines on a number of adjacent exchanges is done without using a dialling code.

The largest LNS in the UK is that for the London telephone area - formerly known as the London Director area. Here, several million subscribers can call each other by dialling a uniform code. Thus for example anyone with a number in the range 020-7xxx xxxx or 020-8xxx xxxx can call London Transport Enquiries by dialling 7222 1234.

Smaller schemes apply outside London. Uxbridge, for example, has the STD code 01895. Uxbridge exchange is the parent for Denham, Harefield, Ruislip and West Drayton; anyone connected to any of those exchanges can call any of the others without having to prefix the number with 01895. This is achieved by giving subscriber lines on each exchange different prefix numbers, thus: all numbers are six-figure; Denham numbers start with 83, Harefield with 82, Ruislip with 67 and West Drayton with 44. Uxbridge numbers start with 2 or 3. All calls must have all six digits dialled - even if a subscriber is on Denham exchange and is calling another subscriber on Denham exchange, they must still dial 83xxxx.

Incoming calls from any other exchange for a subscriber on any of the five exchanges must all be prefixed with the same 01895 code.