The first question is "What is it discounted from?"

Usually the answer is the lender's own Standard Variable Rate (SVR). This is usually a couple of percentage points higher than the inter-bank offered rate, yet it does vary significantly between banks.

Discounted deals are usually temporary and at some point your interest rate will revert to the lender's SVR.  Some discount mortgages look very attractive with their low initial rates, although it's worth noting that unlike a short term fixed rate, a discount rate can go up or down in line with the Bank Of England and other banks.

It's also worth noting that you can get a discount off a tracker rate rather than the Standard Variable Rate. As an example, if the tracker is base rate + 0.75 and it is discounted by 0.5% for the first two years, you will pay base rate + 0.25% during that time.

Pros: It's cheaper than the Standard Variable Rate.

Cons: The discount tends to last for a short (ish) period (typically 2 or 3 years). Plus, as you are linked to the SVR, you could lose out when it comes to Bank of England base rate moves.