You only really need to do the calculations until 31/7/11 because then you will be able to take on any mortgage without the early repayment penalty. You should also stop saying "added to the new mortgage" as if it means that you don't have to pay. I will do the calculations as if there were exactly 2 years to go.
two years at 5.29% on £124k = £13119
two years at 2.74% on £124k = £6785
Difference = £6334
Fees = £4813
Saving = £1512
My feeling is it is marginal whether the saving will be enough to make the switch worthwhile. You would certainly need to be sure that there wouldn't be fees for anything extra (valuation, solicitors, etc). You also need to be aware that different lenders calculate their rates in slightly different ways (2.74% is a bit lower than I'd expect - if you used 3.35% in the above calculations, there would be no saving).
The calculations are approximations for several reasons including because, while there is £124k outstanding now, there will be less outstanding one or two years from now.
In your shoes, I might wait until 2011 and see what the current lender could offer to persuade me to stay. I would look at the other options then.