Hull Trains once proposed a service from Grimsby via Lincoln to Kings X using the Joint Line and to open a station at Donington called "Boston Parkway"That is a reasonable proposal, but it doesn't need a new line, just a station re-opening. It could be marketed as Donington & Boston Parkway.
Bids to re-open the Louth-Firsby line and Mablethorpe were made in the 3rd round of the "Restoring Your Railway" competition for funds, and were unsuccessful (not surprisingly).
@backontrack "We should not be closing rail in 2021."
That would have been hasty, but sadly there will be a need to close/mothball lines in 2022.
It`s possible to operate 2 trains an hour each way under the present arrangement. it happens on Summer Saturdays at various hours .I doubt the cost of constructing a chord from Helpringham towards Boston would be beneficial. Consideration for upgrading the single line between Hubberts Bridge & Boston also needs to given, with regards to capacity along that route.