Thank you for your reply.
Just to confirm I originally had a Thermal Image Survey done and after he imaged the property externally I turned off the heating, he then put a blower on the front door to produce a negative air pressure internally only (any air leakage will then show internally). After some work was completed I had a had another thermal Survey done to confirm if the works were successful or not. I've not had an air test done but the Thermographer can normally tell if your property is air tight or not by how much he needs to turn the blower up on the front door up to maintain the negative air pressure internally.
I'll try to upload some imaging if I can.