You normally just have to outline major events like investigations, xrays and consultant visits, what they were for, whether they were normal or not, and when they occured.
Admitting to coughs and colds is totally normal. I have had insurance accepted for a mortgage without any doctor being written to as there was nothing to report. Always be truthful though, as false info can nullify the policy. Also remember, your GP is obliged to always be truthful when reporting your health. They cannot leave out or couch something in a favourable light.