Regulations for buried cable in the UK

I'm running a cable from my house to a site in my back garden where I am building a shed. The length of the cable run is about 7-8 metres. I have steel armoured cable which is OK for direct burial.

Is there any regulation for the UK about what depth the cable needs to be buried to? I've started digging a 'slot' but it is really hard going due to the number of stones under the turf.

This is the cable I am using: https://www.amazon.co.uk/gp/product/B07B7DJZL8