Where can get a 20 watt round led driver with a 12v output ?

[Avo Mk8]

The cheaper option comes really close though but at 18 Watts, they're just not gonna do it.

You get 3 of the little 18watt PSU's for your single purchase costing £7.50!
I intended to mean you put at least two of those supplies in each light fitting (ie giving you 36W of power) wiring each supply to roughly one half of the lamps in each fitting.
You would need to make two purchases (£15) and you would have 2 PSU's left over.
But if the wiring does not allow you to split the load like that, then obviously this is a non starter.
Sorry I wasn't clear!

From what I can glean from the net the wattage should be marginally greater or equal to the demand.

Yes absolutely correct!

 

[brianmoooore]

Is there any chance of fitting the PSUs remotely from the fittings?

 

[davesparks]

The led's wont run off the original transformer, thought I'd give it a go but they go mental !

In what way do they go mental? What exactly happens?