Yeah when you change your insurance, sometimes they are lazy fooks and dont add your carto the database for like upto 5 days!! I know when I changed my insurance over to the Rover it was on the database the next day... but when I did the 306 it took like 3 days to go on.
You can check if it's on at www.askmid.com
As stated, it's not the police's fault, they are merely pulling you find out if you have insurance or not, as it is coming up as you don't... this helps prevent people from driving without insurance.
I got pulled last year lol, for driving without valid tax. What had happened is I had bought me Rover without tax, so I plodded off the post office and got meself some tax like 3 days before the end of the month... then the final day of the month I was pulled for driving with no tax and showed the kind office my tax disc and receipt. Unfortunatly it turned out the tax disc wasnt valid till the next day (1st of the month)! However my argument was it did'nt have a start date, or a note on the receipt, just an expiry date.
Anyway the kind officer let me be on my way with the advice not to drive with it for the remaining few hours of the day unless absolutely nessecary as id probably be pulled again and I might get a copper who is just out to get everything he can lol.
I don't understand why they dont print a start date on the tax disc's but oh well! Not the police's fault and not my fault.