This should clear thing up a bit. You only need to declare cash over 10K Euro (includes cheques and bankers drafts) if it is arriving from or going to a country from outside of the EU
HM Customs (UK) State
If you are arriving in the UK from a country outside the European Union (EU), or you’re leaving the UK to travel directly to a country outside the EU, you must declare any cash of 10,000 euros or more (or its equivalent in other currencies) to customs officers.
You only need to declare cash if you are carrying 10,000 euros or more (or the equivalent value in other currencies) AND you are:
1. entering the UK from a country outside the EU
2. leaving the UK to travel directly to a country outside the EU
If you are entering or leaving the EU through an EU country other than the UK, the declaration is made in that country.
When declaring cash the EU is:
Austria, Belgium, Bulgaria, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Gibraltar, Greece, Hungary, Ireland, Italy, 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).
Definition of cash
The term ‘cash’ covers:
notes and coins in any currency
bankers’ drafts
cheques of any kind, including travellers’ cheques