2007 Vauxhall Meriva i think the head gasket has gone

It may well be a head gasket , but those Vauxhall engines are bad for emulsified oil , frothy oil on the cap due to engine breathing problems which is very common and not major . If head gasket gone the oil will either go into the sump and show on dipstick as increased level and coffee coloured or blow out the back with excessive white smoke . If in doubt a block test will verify if gasket gone or not , but really need car running to carry out the test .If coolant in sump it needs drained off , oil and filter changed .But many , many reasons for none start .If engine turning over o.k , you need to do the basics and check for spark and fuel firstly .

P.s

You usually find the breather hose choked with sludge like under the filler cap also .