Bought this drop bolt from amazon as we needed it for the side driveway gate. Couldn't find a bolt long enough to do the job anywhere in B&Q, Focus, etc so went for this one. Pricewise it seemed to be the cheapest on the net.
Good sturdy piece of hardware that keeps the gate secured into the driveway when closed/open.
Subsequently needed another one for the other gate and found it in my local hardware shop for half the price. That'll teach me not to support my local independent hardware shop in the first place.