Responsibilities of a new agent taking over a tenancy from a previous agent

Guarantor

We bought an apartment with tenant in situ. As soon as we bought it, we discovered the agents who now handled our account had taken over from a previous agent, who was being most unhelpful. It was discovered that the tenant was already in arrears and the guarantor had not been chased. Our agent advised us to give the tenant notice, which we did, and he left. However, we then discovered that the flat was left extremely dirty for the new tenant, a bed had been broken, and now we discover that he had not paid his electricity bills, information which was apparently first conveyed to our new agent back in June at the outset of the tenancy. They had failed to let us know this.

The agent's response to date has been that the Guarantor was not contacted during this time, and that since the whole deposit was taken to cover the arrears, there was nowhere else to turn for re-imbursement or to pay cleaning costs.

Does the current agent have any liability here for not initially contacting the Guarantor and drawing up a new agreement? They are saying that since the Guarantor signed his agreement with the previous letting agent, they (the current agent) can do nothing.

We are currently facing an electricity arrears bill of nearly £1,000, some of it dating back to June when our current agents first became aware of it but which we only received this morning.