Hello I am a solicitor of over 15 years experience. I will try to help you with this.
If the summer house is built on your land and in accordance with planning permission, building regs etc why do you need to do anything? The land is already yours and so therefore is any building on it.
When you say deeds I take it you mean the entries in the land registry on the assumption this is registered land (it is a long time since I have come across unregistered land). The answer is yes.