Where a creditor covenants with some co-guarantors not to exercise a power of sale over charged property and not to take action against those co-guarantors, non-party co-guarantors are discharged from their guarantee obligations because the implied condition that security be maintained for the benefit of all guarantors is breached. A solicitor who acts on a transaction affecting guarantee security owes a duty to advise the client of the risk that the transaction may discharge co-guarantors, even where the retainer does not expressly extend to the later transaction. Where damages for loss of a guarantee claim involve multiple contingencies, each probability is assessed separately and combined to value the lost chance.
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