Slitherine

I've been playing a game where I occupied the UK, and have ever since been dealing with a swarm of partisans there. I have several corps of infantry and some garrisons to deal with the problem, but they are hard to snuff out, particularly in the winter months, and they have a nasty habit of appearing in any unoccupied city. That is particularly tedious, as the game model for rail transport makes it impossible to rail units to deal with the problem.

In short, I think that on the sliding scale, the number of UK partisans is over on the 'way too many' side. Would it be possible to knock them back by 1/3 or 1/2?

Players who don't use garrisons can definitely suffer from partisans. This is realistic as Germany in the last war had to use an inordinate number of troops to hold down the indigenous population, who for some reason resented being occupied by the master race.
Personally, I garrison cities, wait for partisans to turn 'red' then massacre them. My pet peeve in this regard is that every time I take garrison troops away from a Polish city, a partisan unit almost immediately pops up. In my last game I lost Lodz twice in this way.

A reasonable point, although I will dispute both elements.

In terms of game play, having to garrison every single UK city is prohibitively expensive for the Axis, and furthermore, garrisons are hard on your manpower numbers, since they take 5 manpower units.

In terms of numbers of Axis units tied down by partisans, this is more a product of post-war mythology than reality. All of the post war non-German countries created a resistance story – it's human nature to expand your role in the victory ex post facto.

As Keegan noted in 'Six Armies in Normandy', of forty-some German divisions in France on D-Day, exactly none of them were involved in anti-resistance work.