Seems there is a petrol thief on our street or I am totally over reacting

! I only noticed this the other day but the thieving could have been going on longer.
Range 12 miles, so I stuck 50 quid in which brought it to nearly 3/4 full. A trip to work and back (motorway) 18 miles, next day I start up only 1/2 a tank.
Its never used that much I think.
A friend gives me £10 for picking up some tables, so I put the £10 in as I am going on a 100 mile round trip today. The fuel filler cap is loose, I always 'click' tighten it.
I lock the car and try to open the fuel cover cap to which I can do with surprising ease despite a locking pin coming out.
Hmmm... I think, so off I trot to Halfords to buy a locking fuel filler cap! £15.99p (yeah expensive but so is fuel).
I have also noticed that you can get a hose pipe or fuel line down the fuel filler neck and actually get petrol out, so I think someone is helping themselves to the odd gallon or two.
I haven't cleaned the car for a while, nor have I filled it up much above 1/2 tank. So maybe these petrol thieves are cleaver enough to notice my finger marks along a dirty car near to where I fill her up and thought, oww.. he's filled up.
I have actually thought as of late, god this car is using some fuel, I know its a 3.0 V6 but it shouldn't be using so much lol.
Looks like they'll have a nice surprise when they try it again.
