I say again, there are no extra requirements other than to complete the three required 100nm legs in a single day. No signatures, no requirement for controlled/licensed airfields, no requirement to be in the UK, nothing.
FYI I did mine in South Africa between three uncontrolled unattended fields. I kept the receipts in case the CAA queried me (this is a good habit to get into anyway), but all they wanted to know is the date of the flight and to see the log book entries.
Cheers!
foggy.