There were 4 tenants in a shared house (Let's call them A, B, C and D), all on the same contract (assured shorthold tenancy). One of them (A) leaves before the end of the contract and finds a replacement (E) - the landlord agrees - and the replacement tenant (E) continues the contract. Soon after, a different tenant (B) abandons the property without finding a replacement, and the landlord is forced to look at the other tenants to recover the rent, as they are all on the same contract.
Clearly, C and D are contractually responsible, but who out of E and A is also responsible? Please explain your answers in detail, referring to English law.