It will continue to leak, and must be replaced.
Personally I'd just forget about the previous roofer, its probably not worth the hassle pursuing him or the surveyor over a relatively small area of roof.
Get a professional roofer in and if you want a 'slate look' then you can use Redland Cambrians at that pitch without any issues.
It should cost around £55 per m2 supplied and fixed.
Perhaps your supplier of the Hardrows will take them back into stock, they should come off undamaged.
Personally I'd just forget about the previous roofer, its probably not worth the hassle pursuing him or the surveyor over a relatively small area of roof.
Get a professional roofer in and if you want a 'slate look' then you can use Redland Cambrians at that pitch without any issues.
It should cost around £55 per m2 supplied and fixed.
Perhaps your supplier of the Hardrows will take them back into stock, they should come off undamaged.