If your windscreen is cracked or chipped it may fail its Mot test.
Any chip larger than 10mm (approximately the size of a £1 coin)
which is directly in the drivers field of vision, will result in a
failed test. The defined field of vision is the area that is within
the sweep of the windscreen wipers and 14.5cm either side of the
centre point of the steering wheel. Any chip larger than 40mm within
the rest of the area of the sweep of the windscreen wipers will also
result in a fail.
Even if the chip is not big enough to warrant an MoT failure, it is still well worth getting the windscreen repaired. The reason for this is that the chip may spread and result in a cracked windscreen. Having your windscreen repaired will not usually be too expensive and you may find that it is automatically covered by your car insurance without you losing your no claims bonus. Some repair companies such as Autoglass will even send the invoice to the insurance company direct.