Hi, I thought there wasn't an actual law so had a check anfd found this:
'There is no law which states minimum age that a child can be left alone but it is an offence to leave a child alone when doing so puts the child at risk. The NSPCC recommend that most children under 13 should not be left for more than a short period and that no child under 16 should be left overnight. They suggest that parents consider the following before deciding to leave a child alone:
The age of the child
The child's level of maturity and understanding
The place where the child will be left
How long the child will be left alone, and how often
Whether or not there are any other children in the household'