It's a single digit but it could result in a big premium on your insurance and wipe thousands of pounds from the value of your home - welcome to the latest battle of the postcodes in Whitton.
While the majority of people living in Whitton, within the borough of Richmond, have TW2 postcodes, hundreds of households in 34 streets have TW4, or Hounslow, postcodes.
It may not seem like a big deal but it is when you consider postcodes are used by insurance firms to calculate bills and by estate agents to work out how much your home is worth.
According to residents, a TW4 postcode can add £100 to the cost of your annual car insurance and wipe £30,000 of the value of a three-bedroom house.
To make matters worse, those living on the 'wrong' side of the artificial postcode border in Whitton are still paying one of the country's highest council tax rates for the privilege of living in the borough of Richmond. The annual council tax bill for a typical 'band D' property in Richmond is £1,590 - £200 more than in Hounslow.
That's why Lyn Adams-New and Michelle Phelan, who both live in Conway Road, Whitton, and share a TW4 postcode, have launched a 'We Want to be Whitton' petition to finally get Royal Mail bosses to change that all important figure.
"We live in Whitton, but because of the Royal Mail we are labelled with a Hounslow post town," said Mrs Adams-New, a 55-year-old bank credit controller.
"This can impact in a number of ways, including house prices and insurance. Most companies or individuals use the postcode to determine values or costs and we are adversely affected by a decision taken by the Royal Mail decades ago."
The campaign for a Whitton postcode is nothing new but has been resurrected by residents following last year's Royal Mail stock market flotation, which they hope may make those in charge more responsive to customers' concerns.
The petition is due to be presented at tonight's (Tuesday, January 21) meeting of Richmond Council by Heathfield ward Liberal Democrat councillor John Coombs. It has also been presented to Twickenham MP Vince Cable, who has previously raised the issue in parliament.
Lib Dem candidate for Heathfield ward Michael Wilson, who is supporting the campaign, said the least residents and councillors expected this time was to get a face-to-face meeting with someone from Royal Mail, rather than being fobbed off with a letter.
It's not just in Whitton where postcode wars are being waged, with a number of households in Twickenham unhappy at having Feltham sorting codes for similar reasons.
A Royal Mail spokeswoman said: "The postcode is a Royal Mail operational tool designed to ensure the accurate sorting, routing and delivery of our customers' mail. Postcode boundaries do not necessarily reflect geographical or administrative boundaries.
"Royal Mail does not normally change postcodes unless there is a pressing operational reason to do so though, under the code of practice for postal addressing, there is a process for customers to request a change."
You can sign the Whitton petition, which already has 160 signatures, at http://www.trlibdems.org.uk/we-want-a-whitton-post-code.