I think you have answer now. It is a common mistake to believe that in this fair land we require 500 ft above ground (as is the case in many other jurisdictions). Open countryside or over sea at five feet is legal if a little questionable in terms of safety providing that you are not within 500ft of those items mentioned.
There are a few exceptions to this beyond take off and landing including Rule 5 exemptions which can be used for your own non public, non paying air display if you so wish. A few locations has such exemptions which can be used for display practice. You can apply for one both on and off airfield if you wish to fill in the forms and hand money to the CAA.