There was a lot of money spent on the North London Line re-electrifying it to 25kV and electrifying the West London Line for the Eurostar Regional services. Much of the loco hauled regional night stock sat in Northpole right up to 2007 when Eurostar moved out.
The regional services were the Government of the day form of attempting "levelling up"
IIRC▸ the NightStar stock was sold to the Canadians in 2000
I think the credit for the day and night services is probably more due to
BR▸ than the
UK▸ Government, but indeed, it was arguably an attempt to make the
Channel Tunnel 'relevant' to the country beyond London.
Their failure was largely down to privatisation, which took them from being financially dubious, but sustainable within the broader BR entity, to insanely expensive as standalone services, and very visibly so, as they would probably have needed a heavy subsidy.
There's also the question of how well the 373's would have worked out technically beyond London (
GNER▸ did have them for Leeds services, but they were highly restricted in terms of route) and whether the customs/immigration issues would have worked out.
And then there's the question of how long a trip like Manchester to Paris would have taken, crawling round the West London line then across Kent on third rail. Remember also that the budget carriers like EasyJet and Ryanair were starting to make inroads at the time.
Don't forget also the security concerns of the time - the Channel Tunnel was felt to be a prime target for the IRA, and I'm sure that the security services would have been concerned that the 'north of London' services posed a soft target.
All that said, it is very interesting to ponder what might have happened had work on
HS1▸ started earlier and BR's privatisation been put off a few years. Would HS1 with a decent connection to the
ECML▸ and
WCML▸ have made Birmingham/Manchester/Leeds services credible, and would that have created momentum to build new
HS▸ lines north of London rather than upgrade the WCML?
Of course the other Eurotunnel question is if BR's privatisation had not taken place, might it have been the saviour of wagonload freight? But that's another matter :-)