Most garages can do a 'block test' for you.
This involves a blue chemical in a container on the top of the coolant header tank, fumes from the cooling system are then drawn in through the chemical.
If the head gasket has failed (or the cylinder head cracked) and hydrocarbons are getting into the cooling system the chemical will change colour to yellow.
Usually your local garage won't charge much for this. (perhaps just enough to cover a couple of pints for later).
Takes all the guesswork away - costs pennies (relatively speaking) and takes 10 minutes to carry out. I get mine from the local Snap-on bloke.
Yellow = spanners and wallet, stays blue = reach into fridge for a cold one