[roKWiz]

Originally Posted by Crazy Dazz

L-blocks are precast reinforced concrete sections, in the shape of an 'L', where the weight of the soil on the base holds the upright in position.

I want to achieve another ~1m of retaining, in addition to the ~1m already there

So 2 mtrs high. As others have said here you need to talk to an engineer or seek advice from a company who specialize in these manufactured blocks.
(who will usually direct you to one of theirs)

If the neighbouring property is already built 1 mtr high how do you plan on finishing their side of your extra 1000mm ad on. It would then need to be freestanding above the 1000mm mark or is there an embankment above whats already done.

Other ways beside modular blocks are pre-cast concrete like arm79's pictures below or staggering 500x500x2000 stone logs, both would have to be built in front of whats there now.

With engineering approvals, I've built several retaining walls upto 2300mm high using traditional drystone methods. Obviously strength and drainage are the most critical aspects involved.