Original music appears to be “We will down with the French” (30 years' war patriotic song). Recording: lasses_of_portsmouth-wewilldownwiththefrench-009.mp3.zip

Triple minor or 3C set, proper

A1 C1 2h Turn your Ptnr all the way and cast off into second place while 
   C2 move up. C1 and C3 hands 4 round
A2 C1 2h turn again all the way cast up to top of set & hands 4 at top with C2
B1 C1 lead thro' the C3 & cast up into middle then lead up thro' the top and 
   cast off to finish in middle place
B2 C1 and C2 Right and Left all the way around
   (In 3C set, C1 move to bottom at end of R&L and C3 move up.)

From John Garden:

Lasses of Portsmouth to the tune for 'Fete Champetre'

A triple minor dance from Thompson which found its way into the Apted collection.

Although the dance is only discernible in the cabinet mirror behind the talking actors, is can be followed (up to the point when, curiously, there is a moment when the A part of the tune is repeated a third time - doubtlessly the result of some editing).

If you want to try the actual dance which went to the tune 'Fete Champetre' in Thompson's Compleat Collection, vol.4, 1780, try this reconstruction:

   A1 Turn your Part. right-hand with 8 walking steps
      or 4 travelling steps then left hand turn same
   A2 Just 1s lead down the middle with 8 walking steps 
      up again & cast off with 8 skipping or travelling steps
   B1 The 1st lead up while 2s take hand behind them, 
      and then go left as a couple, followed by 2d & 3d Cu. 
      Promenade quite round till back in original position
   B2 Cast off one Cu. so, with 8 walking or 4 travelling steps, 
      1s return to middle progressed position & quickly right & 
      left at top to go, with just 2 walking steps or 
      1 travelling step for each of 4 sides, all the way around 
      and back into progressed place. 

A video shows yet another version, I believe to Fete Champetre.
https://www.youtube.com/watch?v=IUFVv3dbueI