Hi Phil
I don't have a British army, but must have played against them in FoGN 20+ times.
IMO, Brits are toughest when they take the minimum and cheapest artillery and cavalry units they are allowed, and go for mainly small veteran infantry units that are tooled up with rifle skirmish, or artillery, attachments. I would leave out the Guards/Scots/95th rifles as being too expensive.
I have never managed to break through a reasonably solid line of such units (in tactical, in my view you should only form extended lines if on a hill or if needing to occupy space). Basic British tactics are to advance to 6MU, shoot opponent to disorder, then charge and/or advance to 2MU and rout them with the bayonet/close range volleys.
Given the output of fire at 6MU, and the ability of British veterans to rally their own disorder, the only way to counter a solid British infantry line that I have found is to use your better French maneouvreablity and come in at an angle to the British line, on one flank, and then roll them up unit by unit. If the Brits can secure their flanks on towns etc, it's pretty hard to beat Wellington and his boys.
I see you tried to oppose soem French Guard Cvaalry with Hussars in one game, it would have been better just to park a unit of veteran infantry in front of them and dared them to charge. I've found that simply throwing cavalry units at the middle of a British infantry division usually means dead cavalry. By the way, with steady vets there is no need to go into square in your movement phase, you can (usually!) safely rely on forming emergency square without cohesion drop when/if charged.
If enemy mass up artillery against you, light infantry in skirmish formation is the counter. If none are available you could try a rash cavalry charge. Probably this will mean dead cavalry, but you always have that chance of closing and – if you can – this is one dead artillery unit. If you get repulsed, oh well they were only brit LC anyway and they bought you time and covered your infantry for a bit.
Unless you go for the the massed British Guard/HC option (1815) you will tend to be outnumbered and beaten if you try to indulge in a cavalry fight. Playing French or Austrians, I will seek out British mounted that come out to play, looking to swamp them for easy kills.
The more experianced British opponents I face tend to leave their mounted in a 2nd rank (well back if they are impetuous), either to enagage disordered enemy cavalry passing around squares, or to wait for opportunity charges late in the game when the opposition formations have been broken up a bit with plenty of diordered/wavering targets.
anyway, enough rambling from me
Kind regards
Brett