Rover 25 fuse blowing

Well I wouldn't take it as gospel that it's that particular wire, even if it's a known weak point it may not be that one. (However if it goes between the body of the vehicle to the boot lid through a flexi then I'd look very carefully at that point - classic failure point where it hets kinked and unkinked all the time.) I'd give some general abuse and yanking about to the various wires involved and see if I could replicate the fault happening. Follow the wires through if possible to try to find insulation damage. Where possible look for potential shorts to ground/chassis in the bits the circuit is supplying (bulb receptacles etc.). Maybe selectively snip a few wires to see if isolating various bits of the circuit made the fault go away. Or be really smart and put low-amperage fastblow fuses in each of the lines and see which one is blowing? Just a few random thoughts really.

Dur...rereading this, it's now obvious that you're talking about a body-to-boot-lid flexi. Just pull the flexi off at one end to reveal the cables inside. A visual examination should tell you which ones are in a bad way - bear in mind this isn't just a break of the conductor within the insulation, this is a case of the conductor finding its way out through the insulation and onto something it shouldn't be touching to cause the short. Make good the connection by soldering it if necessary; repair the insulation with tape or heatshrink.