I wish people wouldn't keep bringing up the "log book" V5 or "registered keeper" as if it has any relevance whatsoever. How many questions and answers need to be posted on here before that sinks in?
Whether you own the car or not is a matter of facts. On balance from the facts as given I'd say you do but given you don't have possession of it you are going to have a hard time getting it back without co-operation. I assume by "receipt" you mean "invoice". If the car is invoiced to you then it's fairly likely you will be presumed to own it though your (ex) friend might claim it was bought as a gift to him. If by "receipt" you just mean you have a literal receipt saying received money from tan27 in payment of car then that's less compelling as payment isn't necessarily proof of ownership.
Possession of the MoT certificate has no relevance at all. If friend isn't going to either pay or return the car then you will presumably have to either take him to Court to return "your" car or push for payment of the amounts due. Legal advice needed though.