The Variable Rate
The 'Variable' rate means either the lender's standard variable rate (SVR) or those rates which track an external rate (such as the Bank of England base rate or LIBOR) or tracker rates. 'Variable' means the rate can go up and down.
Pros
The rate you pay may fall if mortgage rates in the market fall - this means your payments may go down. A variable rate without any special incentives may allow you to repay some or your entire loan without having to pay early repayment charges.
Cons
Your payments may increase if mortgage rates rise. So unless you can afford increases in your payments, you may be better off with a mortgage where the rate is fixed for a period of time (giving you time for your income or earnings to increase).