Well the bleeping and “low brake fluid” warning finally got on my nerves and I ordered a switch for the handbrake for my W reg 110 HDi from the local dealer’s, part number is 6339.19 for my car and it cost £3.09. Old one on the left, new on the right. Please excuse the rubbish pictures, which were taken on my phone's camera, wife was using the "proper" camera.
Tool list:
T20 Torx bit/short-handled driver. My driver was too long

and access to the screws is quite tight so I used a 7mm ratchet-ring spanner to turn the bit. You could use a pair of pliers or mole-grips.
10mm deep socket, extension bar and ratchet handle.
Thin bladed flat screwdriver
Medium bladed flat screwdriver.
Ok, first thing is to move both seats fully forward to gain access to the 10mm bolts on the back end of the central console, one each side.

Move the seats fully back now.
Next, using the thin-bladed screwdriver, lever the back of the ash tray panel up and withdraw the whole thing, remembering to slide the lamp holder down and out.
Lift the front of the gear stick gaiter and unclip the back end, then simply lift it up till it covers the gear knob.
Using the Torx bit, remove the two screws securing the side trim (one screw on each side) shown in the photos below
Left

Right
The trim is now held on by a plastic tag
simply push down with a flat-bladed screwdriver whilst pulling the side trim outwards around about the same location.

This will also release the tags on the back end of the trim, near to where it abuts against the console

it will be a bit tight but persevere. The front end just clips around the heating vent pipes and both trims are then easily removed. You might find the vent pipes come out, don’t panic they’re easily replaced during the re-build.
Remove the two 10mm nuts from the front of the console.
Lever up the front of the plastic trim immediately in front of the hand brake lever, and remove it.
Likewise, lever the back of the coin holder/airbag switch up, disconnect the switch wiring and remove the whole thing.
Then lift the back end of the console up towards the front of the car (after removing the centre armrests if you’ve got them), watch out for the cigarette lighter cable which you must disconnect. I didn’t need to fully remove the console but just jammed/propped it up on the passenger seat. This is what you see underneath
The offending switch is under the rubber boot and the only way I could find to get at it was just to pull it over to the right.
Here’s the switch in place, you’ll notice I’ve already unplugged the wiring connector, which simply pulls off towards the rear of the car. Make sure the hand brake handle is pulled up as far as it will go.
Getting the old switch out is a bit tricky, in that you really need three hands. One to hold the rubber boot out of the way. One to push the whole switch assembly forward with a screwdriver until the back end is free and one to push down on the switch plunger. Once the back end is free, push the switch backwards to free the front end. Removal of the switch is just(!!) a question of wriggling it out of position. I didn’t need to slacken the handbrake cable to give me more space by allowing the handle to come up a bit further, so I don’t know if this is feasible if you’re really struggling in the confined space.
As you saw earlier the new switch has a large flat bit on top of the plunger which make fitting it equally as hard as the removal. Again, careful wriggling gets it in place and pushing the back end into the bracket first, then the front, locks it into place.
Then it’s just a case of putting it all back together again.
Re-connect the switch wiring.
Reposition the console into it’s proper place, whilst remembering to to re-connect the cigarette lighter cable. Fit the coin holder/airbag switch into it’s location (front end first), reconnect the switch cable and then push the back end down into it’s location.
Refit the back of the handbrake lever plastic trim into place then push the front down.
Refit the 2 10mm nuts but don’t fully tighten them.
Refit the heater vent pipes if they fell off when you removed the side trims, they clip over the front then you just position the tag towards the rear, into the console.
Refit the side trims by getting the front end clipped in place and then relocating the plastic tags on the rear, so that they locate behind the console, then push the locking tags into place.
Refit the two Torx screws (wriggling the console/ side trim to align the holes). Once fully in place move the seats forward and locate then fully tighten the 2 x 10mm bolts at the rear. Now tighten the 2 x 10mm nuts at the front, relocate the gear lever gaiter and replace the ashtray after refitting the lamp holder (if memory serves me correctly, it’s slightly D-shaped when you look down from the bulb).
That’s it, total time of about 30-40 minutes and no more bloody bleeping when you put the handbrake on. Job’s a good un.
Cheers
Tim