When we go away a neighbour comes in twice a day to feed and muck out and check they are ok. Your legal responsibilities are :
Duty of person responsible for animal to ensure welfare
(1)A person commits an offence if he does not take such steps as are reasonable in all the circumstances to ensure that the needs of an animal for which he is responsible are met to the extent required by good practice.
(2)For the purposes of this Act, an animal's needs shall be taken to include—
(a)its need for a suitable environment,
(b)its need for a suitable diet,
(c)its need to be able to exhibit normal behaviour patterns,
(d)any need it has to be housed with, or apart from, other animals, and
(e)its need to be protected from pain, suffering, injury and disease
and I doubt it would be considered you have met point (e) if they were left unchecked for that amount of time so you could be committing an offence under the 2006 Animal Welfare Act.
The RSPCA have a factsheet here:
http://www.rspca.org.uk/ImageLocator/LocateAsset?asset=document&assetId=1232726775616&mode=prd