You need to read this http://www.charlesdowding.co.uk/wp-admin/post.php?post=46&action=edit esp third para of Initial Preparation:
In damp climates such as the UK, I recommend not using mulches such as straw, which allow slugs to hide by day and eat your plants by night. Where slugs are potentially prevalent, compost is the mulch of choice because it does not harbour slugs. Composted beds look ‘bare’ where not growing vegetables, but there is a mulch of compost protecting the soil below.
Permaculturists often recommend straw mulches but British ones should know better. Straw and hay mulches are great in dry climates.
Why are you making such deep beds, 11in?