In ,
informer typed:

"Peter Smyth" wrote

There is an all night Thameslink service from St Pancras to Luton
although the last tube from Stamford Brook will leave around
midnight weekdays.

It's worth noting that if you are travelling on or after May 16th
that that the Thameslink cross London link re-opens so trains will
call at Kings Cross Thameslink and not St Pancras.

I believe that the 'through the night' service to Luton Airport will
continue to leave from the St Pancras (Interim) station.

--
Bob