The UK Government is spending more (National Government Expenditure) than it gets in income (Taxes, Duties, Asset Sales).

This document makes somber reading.

http://www.dmo.gov.uk/documentview.aspx?docname=remit/drmr1718.pdf&page=Remit/full_details

2018-19 needs £123.0 Billion of Borrowing
2019-20 needs £130.9Billion of Borrowing
2020-21 needs £136.3 Billion of Borrowing
2021-22 needs £116.4 Billion of Borrowing

Thus national debt increases by £505 Billion in the next 4 years.