My mum asked me to have a look at her car, as it keeps beeping and flashing a message about topping up coolant. Anyway, to cut a long story short, the coolant system is getting very pressurised, and pushing water out of the expansion bottle, setting off the sensor. Remove the top and water rushes back in (pressure is there even when it's been left for a couple of days!). Bubbles are appearing in the expansion tank, so I'm pretty certain that it's the head gasket, unless anyone can give me another explanation!

Car is a 51 plate, 2.0 HDI 90 307, done 108K miles. Timing belt is due also!

Can anyone give me an idea of what it will cost to get someone to replace head gasket / timing belt?

How difficult is this to do? I've got a haynes for it, and have done quite a bit of work on cars, but anything in particular that causes problems with these engines?

What parts will I need / should I be replacing while i'm in there? So far I've got: water pump, timing belt, head bolts, head gasket, thermostat, (haynes manual says to replace high pressure fuel lines, but is this necessary?)

Also says that the timing belt needs to be tensioned with some electronic tensioning tool. Never used one of these before, so is this necessary (i might be able to borrow one), or is there a cheaper way to get the right tension?