Making payments twice a year would make a slight difference if the interest was added to the capital.
In the first six months you would earn (£10,000 x 4%)/2 which is £200. Add this to the capital and in the second half of the year you would earn (£10,200 x 4%)/2 which is £204. So £404 in total, or £33.67 per month. If you are a basic rate taxpayer no tax would be payable so long as you do not receive more than £1,000 in total from interest payments. If you pay tax at the higher rate this limit is £500 and if you pay tax at the additional rate all your interest income will be taxed.