Self Assessment income tax and national insurance can be paid here.
Have your 10-digit tax reference (UTR) ready and a note of the amount of tax you are paying. You do not have to log into your HMRC Gateway ‘tax account’ unless you wish to. Select Self Assessment. When the various payment options are offered, the one which transfers payment to HMRC the quickest is the first one, pay by bank account
Government Gateway usually takes about 3 days after a tax return is submitted to show the tax payable, and the same time after a payment is received to show this. (It does not mean that the return or payment were not received.)
It is possible for taxpayers to set up their own Time to Pay arrangement online, or to request this by phone.
There is general information on payment of tax here.
Where tax is not paid by 31 January, interest is charged. It is worth making a part payment if full payment is not possible, or and estimated payment if the tax return is not submitted by 31 January, or includes any provisional figures.