Failures of the motor controllers are very common, unfortunately. Has the router been kept in a shed, or somewhere that gets hot and cold as the outdoor temperature changes? If so, it's most probably damp that's destroyed the track of the speed controller variable resistor (AKA 'potentiometer or 'pot': the knob or thumbwheel you adjust manually). It's has a circular track made of compressed carbon, with a carbon wiper, a bit like a pencil lead, and the track can crumble away (like microscopic road potholes), leaving non-conductive gaps.
Thing 1: take it indoors and warm it up thoroughly and get it thoroughly dry. Start by putting it in a sealed plastic bag that you squeeze as much air from as possible. Otherwise if it's cold you'll get a lot of condensation on it as you bring it indoors (BAD). Alternative: take it immediately from the shed onto a hot radiator indoors - must be hot and must be immediately (don't linger in the kitchen for a minute!). Once it's warmed-up the risk has gone.
Let it continue to thoroughly dry out in a warm place for a few hours (overnight), then gently work the speed control knob back and forth end-to-end a few times (no power at this point!). If you feel any mechanical rough patch, that's almost certainly damage. If it's smooth, you might be OK.
Thing 2: Assuming it's intermittent (won't give a stable speed) you MIGHT be able to improve things if you can get at the control pot's carbon track inside the router. If the damage is visible, it's too late, but
rubbing the track in the problem area with a soft pencil (4B is best) might help (don't leave loads of graphite dust inside it though as that's conductive). Don't try this unless you are comfortable with assembly/disassembly of mains electrical equipment. You might get a replacement control from somewhere like Maplins, CPC or Rapid electronics. To do this, you'll need the letters and numbers from the part, (and the ability to solder).
I wouldn't attempt to connect directly to the brushes for a number of reasons. In short, the electronic speed control is unlikely to be feeding the motor directly with 240V mains. It's hard to know and I wouldn't risk it.
Incidentally, for long term storage, ALWAYS wind the speed controller to one end or the other. That places the wiper off the track altogether and will extend its life enormously. I'd guess the best position is leaving it on the fastest speed setting, but it depends on how the pot is used in the circuit, which I can't know from a distance.
Probably doesn't help much, but you never know.
E.
PS: I've got an old B+Q router (Performance Power, Power Pro or sommat - blue with yellow bits, anyway) with the same problem. but haven't had time to look at it. WhenIGetAMo, I'll do so and report back.
