Assuming that you've got no other taxable income, you'd pay hardly any Income Tax.
The first £10600 of income in a year is free of tax. So you'd only pay tax on £1400 (at 20%). So that's £280 tax to be paid across the year, which is equivalent to about £5.38 per week or £23.33 per month.
However you'd also have to pay National Insurance (which is just a tax under a different name). Expect to pay about £9.09 per week or £39.40 per month.
A useful tool:
http://www.thesalarycalculator.co.uk/