Hi Ravima,
This has a number of potential problems, not least being the clause in the purchase contract expressly forbidding it. There is a massive risk factor involved, considering you are tying yourself into the purchase of a property and if you are unable to find an alternative purchaser, you are then responsible for the property you signed contracts on.
The scheme that you have depends on a rising property market and whilst at the moment the property market certainly seems to be rising, that cannot be guaranteed for the future. Therefore, you cannot be guaranteed a return on your investment.
As MOB has mentioned, many builders solicitors expressly forbid this action. I'm sure it increases the costs for them when they have to deal with 2 sets of contracts on the one property etc. What would your increased legal charges be?
Your finances might be better served being put to another use IMHO