WHAT AND WHERE CAN I BUY LEATHER JACKET KILLER?

Emma, your description does not match the grubs that I call leather jackets. Regardless, I would go to a good garden centre and ask them for a solution.

I misread this and thought you were asking where you could get a killer leather jacket and had to click on to see what the answer was!
I agree with bulbaholic, don't sound like leatherjackets to me either - commonest place to find them is in the lawn.

studing your discripton,they could just be leathe jackets, are they short and fat with an armerdilion type sort of skin, if so they are'' jays fluid ,in the watering can ''strenth acording to how bad you have them all over the garden it will nor harm plants or your cat or dog,the budge should not be out there

If they are wormlike and with msny legs they could be millipedes which do no real harm to anything.

Thanks for all you answers! Not sure now if they are what i thought they are? All i know is that there was loads of them, they were like half an inch long, black and some of my grass died.

There was a product called Autumn Toplawn that contained something to discourage/treat for leatherjackets, but I don't know if a) its still available and b) whether it still has something in it to do that. The other two things you could apply to your lawn to kill them earlier in the season have been banned by the EEC.

JustGreen deal in biological water on cures.