Split pick replacements.

Dimarzio's Split-P is very versatile if you want to try a bit of flexibility; looks bonkers, though. Dunkmore Semen offers a more trad-looking range and, IIRC, they now have clips so you can listen in and decide whether the hotter or traddier sound is what you're after.

If you're looking for a cheaper option, Kent Armstrong sound good for smaller dosh and don't forget to look up pups on FleebUS and have them posted in a GPM envelope. Typically half the UK price.

Sorry I got in on this so late. I agree with 1Bass.

You might try the overwound P Bass pickup from Guitar Fetish. It is the GFS brand and for the money it is very good.

Good luck !!!!!!!!!!!!!!!!!!!!

Never too late to agree with me, Jimmy :D , and good to see you in again.

Lee, I had a good look. There's a Fleebshop doing Kent Armstrong, assuming you want the Alnico rather than ceramics (and I think you're the type) for £35 plus £2 postage.
http://cgi.ebay.co.uk/Kent-Armstrong-Fender-Precision-Bass-Pickup-Vintage_W0QQitemZ130181453783QQihZ003QQcategoryZ42455QQrdZ1QQssPageNameZWD1VQQcmdZViewItem?_trksid=p1638.m118

There's even a new PBV (same thing) going in 10hrs on a private auction but note the ridiculous postage:
http://cgi.ebay.co.uk/kent-armstrong-bass-pickups_W0QQitemZ140194648136QQihZ004QQcategoryZ22670QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

but I had a good look at Jimmy's recomm for the GFS Hot P pup. A whopping 16k (the usual DC resistance for an AlNiCo P-pup is 8-10) so it's grunty. $32.95 is so reasonable that, even with the $16 airmail, that comes to under 25 quid. Very tempting and, even as merchandise, it comes under the customs threshold. Certainly worth a gamble, seeing as Jimmy's given them a try.

I see what you mean, Tim; they don't do a 'hot' Jazz. You'd have to settle for the normal AlNiCo P pup and the T06 Jazz bridge pup to get a reasonably balanced output from both.