Sliding ridge tiles between a partition wall

[FBF22]

I live in a terraced Townhouse and on one side of the roof the ridge tiles, that run down the roof between me and my neighbours, have slide about an inch and the mortar is all cracked and crumbling. There is about 15 ridge tiles on quite a steep roof and I would guess the weight of the tiles is causing the problem. About five years ago we had a similar problem when 4 or 5 ridge tiles slide off the roof as the spur was not positioned correctly. So this time instead of just getting someone to reset the hip tiles I was wandering what other solutions could be used - so far I have had the following suggesting

1) Reset the ridge tiles but then pin the tiles individually to the main roof truss
2) Remove the ridge tiles all together and insert a 'Bonding gutter' before renewing roof tiles over the gutter so they butt up together
3) Remove the ridge tiles all together and create a lead valley which would match the front of the house

Can some please advise which of the solutions would work best or even advise of other possible solutions.

Thanks for any help

 

[^woody^]

Fix a hip iron to the end tile at the eaves would be the easiest

or

Use a mechanical fixed dry-ridge system