I believe I remember the government saying they were going to simplify this area.
Seems to be a bit of a failure as there are a plethora of different schemes out there.
You are unlikely to be on the best mortgage but you should make sure you're not close to the worst.
The best for you will depend on your situation but there are things to watch out for.

Early payment penalties - mean that you are trapped in this mortgage. Ma not be bad for a discount/fixed rate period but be wary of a period that extends beyond that on a variable rate.
Yearly interest calculations - this should be rare now as most are daily calculations.

If you have spare cash or then an offset, flexible or mortgage account that is merged with a current account might be best. See the 0% interest credit cards as this will work well with that scenario.
Otherwise a discount or fixed rate depending on your view of future interest rates.
If you are on a variable rate then think about changing.
Have a chat with an advisor - it will be free and he may manage to get a better deal with the same company.

One Account

Whatever happens don't miss payments as this can be expensive and affect your creedit rating.