In general, if you do not pay the rent, then you may be subject to an eviction notice. It is therefore not advisable to simply withhold rent on the basis that the landlord has not undertaken repairs.
If the property is in need of repairs, then you should follow the steps laid out here, which includes first formally writing to the landlord. If the landlord does not provide an adequate response within 14 days, then you can contact your local council.
You do have a right to undertake the repairs and deduct the costs from the rent, however, you should not do this without first taking independent legal advice. You must be certain that the repairs are the landlord's responsibility. If you would like to proceed with this, there is a proper procedure that you must follow. You can read more about this here.
If your tenancy agreement has a break clause, then you may be able to end the tenancy early.
There are rules to prevent your landlord from evicting you because you raise concerns about repairs. For more information, please see this article on retaliatory evictions.
Information on this site is by way of general guidance only and may not apply in your particular circumstances. You should not act or refrain from acting upon information on this site without seeking independent legal advice.