If the seller goes bankrupt, then you need to distinguish between a sole proprietor and joint proprietors:

the legal estate passes to the trustee in bankruptcy, and therefore the buyer must deal with the trustee (and not the seller). If necessary, the trustee could be forced to complete the sale by an action for specific performance, although he would have a right to disclaim (s315 Insolvency Act 1986) if the contract is ‘onerous’ or at an undervalue. If the property remains in the name of the bankrupt, the LR will accept a transfer executed by the trustee (and not by the bankrupt) provided the applicant lodges the evidence required in para 5.2 of LR Practice Guide 34.

whilst the bankrupt’s beneficial interest in the property passes to the trustee, the legal title remains vested in both proprietors as co-owners. The bankruptcy will amount to the severance of a joint tenancy, but the key point is that the legal interest remains in the bankrupt and the other co-owners. Thus, it is the co-owners (including the bankrupt) who must sign the transfer (if the bankrupt refuses, then the Trustee Act 1925 provisions will have to be used to get the bankrupt replaced as one of the trustees). In practice, it is best to get the trustee in bankruptcy to also execute the transfer, so as to consent to the transaction (and so avoid any future argument about the transaction being entered into in good faith, and also acknowledging receipt of the bankrupt’s share of the proceeds of sale, although there is no way to force the trustee in bankruptcy to do so). Source: Conveyancing Handbook (the new, 16th, edition is, as always, indispensable; Law Society; £85).