And the Kiburn crash is actually the Central Line crash at Leyton.
But it show A stock, so cannot be Leyton. Although the picture on the clip appears to be 59/62 stock, so may be a 'stock' (please excuse the unavoidable pun) picture.
The newsreel footage relates to the Kilburn crash (A stock and 1972 stock visible) but there is a brief mention towards the end of the clip to the then-recent crash at Leyton, and it is a still from that section of the report which is used in the caption. The Richmond overshoot in 1987 is wrongly captioned as "Kendal Green" (sic). There was a collision at Kensal Green the previous year, between a 1959 stock train and a class 313.
TfL have had almost no control over the budget and limited input into the scope until very recently.
If, as I had originally understood it, TfL were to have been paid by HCC to build it, and HCC were to carry the financial risk, then there is no reason why TfL shouldn't have done it. But if TfL is to carry the risk, it is up to them to decide whether or not to pull the plug.
Very long term you might be able to segregate the Watford DC from other National Rail services and build stock with the same floor height as the Bakerloo line trains and change the platforms to match. .
Possibly, but then what would happen at Watford High Street if the Croxley link ever happens? It would also require dedicated platforms at Euston (at present LM services can use the same platforms, although they rarely do so)