Init bruv.
-_-
Seriously, you must have road tax at all times. This is easily checked on the DVLA database they can visit and fine you or spot you using ANPR cameras. Road tax cannot be bought without an MOT. Without tax your car must be declared SORN and not parked or used on the road. If it is not declared SORN you will be issued with an automatic £80 fine. Growing the longer you don't pay it. You will have to pay for road tax. The DVLA check monthly. The DVLA/Police also operating clamping schemes for untaxed vehicles on public roads. Your car can be clamped, taken away and impounded and then crushed. You will have to pay release fees which grow for every day it is stored.
Equally you must have insurance at all times. Insurance will not necessarily be made invalid by not having an MOT, providing there isn't a clause stating as such in your policy and providing you can prove that the vehicle was road worthy at the time of the accident (service records, photos, etc). Driving without insurance will be easily spotted by Police ANPR checks that are becoming increasingly common. I spot one at least once a month. Police now have the power to seize uninsured vehicles and are seizing around 1500 each week. The same clamping, impounding and eventual crushing rules apply. Along with the same storage fees and need for you to display proof of insurance before collection. You will automatically receive a £200 fine and six points on your license.
You need to have an MOT on any car over three years old that will be used on the road. The only exception is when driving one to a test center for a pre-booked test. If the police stop you, you'll want proof of the appointment. Of course if your tax has run out you can also drive without tax in these circumstances. Driving without an MOT the rest of the time can result in a small fine, growing larger if you ignore it. No points will be given and as said your insurance can remain valid. Police will easily spot whether you have an MOT certificate with ANPR cameras.