2005 TDV6 120k wont start when cold

Im hoping some one can help on here. I have a 2005 Disco V6 with 120k on the clock. It has been fully serviced through out its life. It has just had its most recent service but wont start when the outside temperature is close to zero.
I have had the last service at an independent garage. They have told me they tried to check the glow plugs but are struggling to remove them but think they are ok. They think the fault is the egr valve and have suggested just blanking it off. The car is not showing up any faults apart from the EGR valve intermitently. Should i take it to a franchised dealer or try the cheap option of blanking the EGR's first? Could any one suggest anything else?

Any help would be great

so they havent checked the glow plugs then??

They said they dont think it was the glow plugs but they dont want to change them because they think they might snap one and then it would be a massive cost to drill out. They said they believe they are OK. Does any one know how much a dealer charges for new plugs to be fitted?

might be wrong but thought you can test glow plug by ther resistance.as for price have a phone round prices are diff area to area