I am assuming that the charge has been registered with the Land Registry.
The house can be sold, however, on sale you will receive the amount that the charge is worth.
The solicitor or conveyancer will know that you have a legal charge when the Land Registration documents pass to him. ( either in paper or electronic form,)
If the charge is registered, I believe the sale cannot go through without you being involved. It may be possible that it could go ahead against your opposition though.
Make sure it was on the Land Registry title & then consult a solicitor if you have lost out.
the house that the charge is on can not be sold without you being notified , when me and my fiance bought our house he owed his mum and dad �15k so the solicitor put a charge on it for them rather than putting them in the deeds etc, when we wanted to borrow some more money of our mortgage company his parents had to sign a form to confirm we were allowed to do this due to the charge