Be very careful about using askmid - the terms and conditions state:
"I am entitled to the insurance information about the vehicle detailed above for one or more of the following reasons: It is either registered/ owned/ insured by me or my employer; I am permitted to drive it; I am an Insurance Broker or agent and acting on behalf of my client.
I understand it is an offence to wrongfully obtain information of this nature without any of the above reasonable causes. If I fail to provide true reasons for acquiring this information I may be committing an offence of unlawfully ..... "
Far better to report it to the police - they can check very quickly and will deal with it if it is uninsured. You can do it online anonymously using Crimestoppers or call them on 0800 555 111
If you're going to report it you may as well just report it without checking - you are allowed to report somebody you suspect of committing an offence, you don't have to know for sure.
I use the Vehicle Smart app to check if a vehicle is taxed and MOT'd. It is free and gives all the information about the make, model, colour and mileage; previous MOTs, the faults and advisories; when the tax and MOT is due.
Very handy when I'm out and about.