If you are travelling to the UK from a country outside the European Union and are carrying the equivalent of 10,000 euros or more in any currency (in cash, banker's draft or cheque of any kind) you will be required to declare this at Customs Control.
Forms on which to make the declaration will be available when you arrive and you will be able to keep a copy of the completed form, which you should keep safely as evidence that you have made a declaration. Please note that a very large fine can be imposed if you do not make this declaration, or provide incorrect or incomplete information.
Note: For the purpose of the cash declaration only, the countries of the EU are Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Gibraltar, Greece, Hungary, Ireland, taly, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, (including the Canary Islands), Sweden and the United Kingdom (not including the Isle of Man and the Channel Islands).
If you are carrying more than the permitted duty/tax-free allowances, or any prohibited goods (eg drugs, offensive weapons, food or plants from outside the European Union, medicines made from endangered species, etc) you must pass through the red channel.
If you are not sure about what you can bring into the UK you should check with the British Embassy or High Commission in your home country before travelling to the UK. Before you contact them, you can obtain some very basic information from the leaflet Travelling to the UK - what you can bring, what you can't, what you must declare.
There is an information leaflet about declaring cash on the HMRC (Her Majesty's Revenue & Customs) website:
Declaring cash when entering or leaving the UK.
Normally, you should not bring food into the UK. Many of the foods you usually eat at home can easily be found in UK shops. For more information, see the leaflet Bringing food products into the UK.
You might also want to look at the UK Border Force's 10 Top Tips for passing through Immigration and Customs control on arrival in the UK.