Hi LR Disco 1 98, ~100000 miles

(I understand the concept of conversation of mass so I know it isn't disappearing really)

Apologies as I am sure that this has been asked many times before.
I am loosing coolant - among other things

When I say I am loosing coolant I mean that I am loosing about 1/2 gallon in just about 30 minutes of driving or so from what I can make out. Basically it is drinking coolant

None of the coolant hoses are leaking, got a puddleof water in a channel of the front cover just behind the water pump. No coolant in footwell (don't think it is heater core leak). Engine temp is just below half on console gauge and I have no smoke (white or otherwise) from the exhaust.

Engine is a bit bumpy on startup sometimes ?? i.e. I can start it and it runs smooth, turn engine off and restart and it is a bit lumpy until you hit the gas and then it runs smooth (new plugs and leads).

Can't think if what else to say except - HELP ??
head gaskets?
freeze plug?

I can't find any leak that looks like this much coolant disappearing.

Oh yeah - topped up coolant, drove for about 5 minutes or so, lost a ton of coolant and not a single drop of coolant leaking from below the engine so if it is going anywhere it isn't going on the floor ???

Any help very much appreciated.

Cheers