Shared boundary wall with the church, what rights do I have?

My garage (England) was broken into last night. The thieves accessed the property from a church that shares a boundary wall, It's a retaining wall that is approx 5 foot high on our side and less than one foot high on theirs. They simply walked over it and were able to scrabble back out with their ill gotten gains.

I'm trying to figure out the best way to secure this easily accessible route (after restraining myself from digging a punji stake pit this morning!) and would love to hear of any experience you lovely lot might have had with the CoE and boundary walls. The cost to raise the height of the wall is significant from a quick search so it'd be great to know if they'd carry any sort of responsibility to cover this cost? I sincerely doubt it but hey, if I just assumed... You know the rest!