After the failure with the hessian grow bags, this is plan B.

I drained about two feet of water from the pond and installed this row of house bricks wrapped in pond liner.  I then backfilled with soil, planted the plants and covered with 10mm gravel.  In deeper parts I was able to use concrete blocks wrapped up in pond liner.  The concrete blocks are shown in the top left of this picture.  The pond is then refilled.

I planted the lilies and Golden club in commercial planting baskets.  The golden club was growing to start with, but now appears to have died, as did one of the lilies.  I replaced the lily with a Gladstone lily which flowered throughout the late summer.  I think the Golden Club was eaten by the Carp before it had a chance to establish.