Tyre LawTyres must have a minimum depth of 1.6mm across 3/4 of the centre tread. The outside edges can be left with no tread. A fine of up to £2500 and 3 points can be given for each illegal tyre.If you drive with damaged or worn tyres you could not only be fined and in breach of your motor insurance policy, but you could also be endangering lives.General Requirements Every tyre fitted to a motor vehicle or trailer must be fit for the purpose for which it is being used and be free from any defects which might damage the road or endanger any person. This means the tyre: must be compatible with the types of tyres fitted to the other wheels must not have any lump, bulge or tear caused by separation or partial failure of the structure.It must not have a cut or tear in excess of 25mm or 10% of the sectional width of the tyre, whichever is the greater, and which is deep enough to reach the ply or cord.It must not have any part of the ply or cord exposed.Note: A vehicle is liable to fail an MOT test if a tyre has any of the above faults or if the vehicle has tyres of different nominal size or aspect ratio on the same axle.Duty to Maintain Each tyre must be correctly inflated to the vehicle manufacturer's and the tyre manufacturer's recommended pressure. ('Run-flat' tyres partially inflated or in flat condition are permitted in certain circumstances.)Tread depth must not fall below the legal minimum. The tread is that part of the tyre in contact with the road in normal conditions. The minimum depth of tread depends on the class of vehicle. Spare tyres There is no legal obligation to carry a spare tyre and it does not have to comply with the legal requirements while it is stowed away. However, when fitted to the vehicle (for example, following a puncture) it must then comply with the law. A spare tyre is not a testable item in the MOT test, though the examiner may draw your attention to an unserviceable item as a matter of courtesy.Penalties Where a vehicle fitted with an illegal or defective tyre is used on a road, a police officer may give the driver a Fixed Penalty Notice or, in Scotland, a Conditional Offer Notice.A police officer has discretion not to issue a fixed penalty but to report the case for prosecution. In law, the driver and the owner (if different) are liable and one or both may be summonsed. The maximum fine which a court can impose for using a vehicle with a defective tyre is £2500 and three penalty points (£5000 in the case of a goods vehicle or a vehicle constructed or adapted to carry more than eight passengers).If a vehicle is fitted with more than one defective tyre, you can be summonsed for each tyre which is illegal. Disqualification is also possible in certain circumstances.