I know I am confused about your home buying and selling contracts, and agree it should change.
In Canada it is a formal contract of sale, clauses can be added in, but must be accepted by the other party, for instance, we agree to sell for xxx dollars subject to financing by xxx date. If the purchaser does not have financing in order by then, the deal can fall through, but neither party can change any prices. The clauses can include inspections, financing or sale of another property, but with a closing date.
I have heard many heartbreaking stories in England regarding deals falling through. It just doesn't seem right that the prices can change once an agreement is made.