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I would be very wary of attaching a positive id to this one.

Psilotanypus females should have 13-segmented antennae, yours appears to be 14-segmented. P. rufovittatus should be much paler than this with the legs and scutum extensively light yellow. It's also smaller than the size you've given above.

I would look out for a corresponding male and try to get a picture of the tip of the abdomen to show the gonostylus, which should be quite distinctive.

In the meantime, using Coe's very out-of date key to the British species, it appears to agree most with P. simplicistylus. That's based on the number of antennal segments, large size and apparent lack of a dark shade across the outer part of the wing. Coe (in 1950!) gives the only county as Lancs and the flight period as May.