Thank you Oliver!!!
Actually this sabre indeed does seem to be a British M1788, however the rather off center position of the blade in the hilt does suggest some incongruence.
This particular hilt form is characteristic of a genre of these light cavalry hussar sabres which indeed were used in Germany, Austria and Eastern Europe in the second half of the 18th century. In looking at this at first I was inclined toward German, but it must be remembered that in this period England was not only adopting these forms, but in many cases blades and perhaps even some hilts were brought in.
With the M1788, in examples I have seen Thomas Gill of Birmingham always seemed to favor the German styling features; the flat top pommel cap usually with a button type dome, and the elongated and narrow rectangular langet which extends above and below the crossguard.
James Wooley who was a contemporary of Gill, seemed to favor a more rounded and raised pommel cap while the langets, also above and below the crossguard was elliptical in shape.
It is also possible that this sabre might have been an import from Germany brought in by J J Runkel, who was a German importer with offices in London who supplied various British outfitters and makers. If this was a Gill example it would be marked, usually stamped on back of blade near hilt.
In this time in England which was just prior to establishing regulation pattern swords (1796) there were of course variations but this example does seem to correspond to those in use by British units c 1788.