If you are travelling to Great Britain and are carrying the equivalent of £10,000 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, if you have not declared it in advance. Look at Government information on bringing cash to the UK for how to do this. Please note that a very large fine can be imposed if you do not make this declaration, or provide incorrect or incomplete information.
If you are carrying more than the permitted duty/tax-free allowances, or any prohibited goods (eg drugs, offensive weapons, medicines made from endangered plants, 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 Government leaflet UK customs information.
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 into Great Britain.