I may have the opportunity of a 2nd job. This would be on a 'self employed basis' I contacted the tax office and they said I would have to fill in a self assessment for which is ok but obviously I would want to pay my extra tax contribution straight away and not wait for the bill to come in? Any suggestions?
You can pay your tax over to HMRC monthly, alternatively you could open a separate savings account to put the tax money in monthly, which you can then use the pay the bill once it becomes due. Just make sure you don't use that money in the meantime.
Once you have registered as self employed you will be issued with a Unique Tax Reference no, once you have this you can pay as and when you like as long as the balance is paid by yhe correct due date
If you employed in your main job you can opt to pay your tax on self employed earnings via your tax code. HMRC then collect the tax the following year from your employed earnings.
If you do not want to do this you can save up the money and make the normal payments on account as and when they fall due. Regardless of what you decide you must inform HMRC of the new job otherwise you are liable to a fine even if the new job does not generate any profits.