You need to get a new tyre straight away anyway.

Apart from being dangerous it's also 3 points on the licence for every defective tyre:
What Are the Penalties for Driving With Faulty Tyres?

In the case of any vehicle, with the exception of goods vehicles and vehicles adapted to carry more than eight passengers, for every offence there is a fine at level 4 of the standard scale with discretionary disqualification with 3 penalty points.
Level 4 currently stands at £2,500 and each faulty tyre is considered as a separate offence, which can really add up. Two faulty tyres equals £5,000 and 6 points on your license, and so on.
How Do I Make Sure my Tyres Are up to Scratch?

The law is quite specific when it comes to tyres, but it’s still an offence that catches out many drivers each year. You must not use a motor vehicle or trailer that has any of the following defects:

• Tyres that don’t fit properly or are unsuitable for use of the vehicle
• Tyres that are unsuitable when compared to tyres on the other wheels (for example: In the UK it is illegal, not to mention dangerous, to mix radial ply and cross ply tyres on the same axle or to have radial ply tyres on the front axle and cross ply tyres on the rear axle. Exceptions can be made for emergency situations but should be avoided wherever possible.)
• It has a tyre that is not so inflated as to make it suitable for the use the vehicle is being put to
• It has a tyre that has a cut of more than 25 mm or 10 % of its section width
• It has a lump tear or bulge due to structure failure
• It has a tyre with exposed cord
• The base of the groove or thread pattern is not clearly visible;
• The tread depth falls below the legal minimum tread depth for car and similar tyres in the UK and Europe which is 1.6mm throughout a continuous band comprising the central three quarters of the breadth of tread and round the entire other circumference of the tyre.
• The tyre is not maintained in such a condition as to be fit for the use to which the vehicle or the trailer is being put or has a defect which might cause damage to the surface of the road or to persons in the vehicle or on the road.