Tradespeople driving vehicles that don't comply with London's expanded ultra-low emission zone (ULEZ) can offset the charge imposed on the most polluting vehicles against tax.
The zone, which was first introduced by the then Conservative London mayor Boris Johnson, has today been expanded to Greater London so it now covers all 32 boroughs.
Owners of a vehicle that doesn't meet the ULEZ emissions standards and isn't exempt must pay a £12.50 daily charge to drive within the zone.
It applies 24 hours a day, seven days a week, every day of the year, except Christmas Day.
The expansion of the scheme has proved controversial with strong opposition from some drivers.
Self-employed tradespeople are among those who have protested, but HM Revenue & Customs (HMRC) has now confirmed that the ULEZ charge can be claimed as a standard business expense by business owners and the self-employed.
In a statement to the BBC, HMRC said:
"Self Assessment customers are entitled to tax relief on travel expenses, including low emission zone charges, if they have been incurred wholly and exclusively for the purposes of the trade.
"When a self-employed individual claims an allowable expense, the amount is deducted fully from their taxable profits."
The charge cannot be offset against tax for .