As you say Jim, every move to extend the tram network in London has failed so far. My former office in Mitcham backed on to the Spratt & Winkle, a 2 car train every 45 minutes would meander past with a dozen or so passengers on board. Later, after it had been converted to tram, a tram would pass every 15 minutes in each direction quite quickly, and nearly always with a decent load.
I was able to see the construction of the Croydon system from the outset and before, and tendered to provide the train replacement bus service during the conversion of the railway to tramway. Arriva beat me on price. There were many problems before the system opened, such as the contractors not allowing for gauge widening on several sharp corner in Croydon, this resulting in track having to be dug up and relaid, and a dip in Surrey Street when trams would derail.
As for extensions, the first few trams were delivered with destinations for Uxbridge, Shepherds Bush, Embankment, Sutton and a few other bits. But then Leon Daniels was in charge of First Group who had the franchise for tram operation at the time, and Pete Hendy, also with First at the time, was later in charge of TfL. Both I've known personally for the lat 50 years or so. What was not all that helpful was the refusal of Croydon Council to allow the trams to run along London Road, hence the circuitous routing round Croydon.
Proposals were in hand at the time to extend to Sutton, as well as along the A23 to Brixton and central London, the A23 being wide enough to take the tramway as it was the site of one of the first tramways in London. The other proposal was from Shepherds Bush to Uxbridge, again a road originally having a tramway. Again objections form the local councils killed the project. but quite why they are so over-engineered is a mystery.
I am aware that they have to take into account the problem of the earth returns causing problems with steel and iron pipework underground. The Luxembourg system gets round that by using battery power in the central area and seems to work quite well. We were lucky enough to visit the Luxy system at an open day many months before it opened. Facilities were over-provided with a view to future expansion, unlike croydon which was built with minimum cost in mind.
The Luxembourg system was largely built with EU money in the form of regional development grants. It's a pity the GLA and UK governments didn't make better use of those facilities to help build London's system.
As an aside, my bus fleet at the time consisted of about 6 Routemaster and a dozen or so box buses. The first time tramline failed their controller phoned me for replacement buses, insisting we sent Rotemasters, he would provide some drivers and conductors. He knew we already had "tramlink replacement service " on the destination blinds as well as Croydon and Wimbledon.