Tony Polson wrote:

The plans are much more likely to gain DfT approval if the DfT does
not have to pay for it. As the West London Tram would be funded by
TfL, the DfT are more likely to approve it than if the money had to
come from their own budget.

There is also the the important point that the WLT is a genuine
transport scheme, the purpose of which is to address the need for
improved public transport in a busy established corridor.

In this respect it is markedly different from several of the schemes
that have failed to secure funding, and which were seen as part of
regeneration strategies.