Female Dark Bush-Cricket (Pholidoptera griseoaptera), a common one and often in gardens etc (along with the Speckled Bush-Cricket). Another couple to look out for are Roesel's Bush-cricket and the Long-winged Conehead (what a great name), both recently spread across most of Southern England up to the Scots border in areas of longer grass. They are difficult to see, but you can hear them, the Conehead has a quiet slow ticking call, a bit like a bike free-wheeling and Roesel's Bush-cricket sounds like a Cicada crossed with guitar feed-back.
I've been hearing them a lot at night,no guitar feedback though Long-winged Conehead is a superb name,now going to look that one up!
We get the bright green ones in the house a lot,some nights it sounds like a jungle in here.