Declaration to customs is required at UK arrivals and departures when a passenger is carrying 10,000 Euro or more between a non-EU country and the UK (including cheques and traveler's cheques).(As of June 15, 2007)
Declaration Form:
Declarations Forms can be obtained from the UK arrival or destination airport, or can be downloaded from the HMRC (HM Revenue & Customs) website. Declarations Forms are not carried in the aircraft.
Other:
Failure to declare cash will result in a fine of up to ₤5000.
For more information, please refer to the Government News Network.