You most likely will not need more than 4-8mg of Subutex at once to relieve w/d symptoms, but if you can tell us how much exactly is a "bag of gear" where you are it will help determine that. Is that .1g, .5g, 1g? It will be much easier to answer the question of how much Subutex to take if you can tell us that. Also, make sure you are in w/d for a little while before you dose with the Subutex so you can avoid precipitated w/d. If you take your Subutex sublingually as directed, it should relieve your symptoms within 15 minutes, 30 minutes max. If after 30-45 minutes, you don't feel 100%, dose with 2mg more and repeat this process until you do feel 100%
The temazepam should help, but I have hear that Clonidine is very helpful with w/d and in the U.S. it very easy to obtain from a doc, so that may be the same case in the UK. Immodium A/D is also very helpful with the physical w/d symptoms. It's an OTC antidiarrhea med that contains Loperamide, which from what I've been told is an opiate that doesn't cross the BBB, so it won't get you high, but will lessen w/d.
Good luck on getting off methadone/heroin and maintaining on Subutex and check out
http://www.bluelight.ru/vb/showthread.php?t=524458 it's the Suboxone/Subutex megathread and FAQ, so there's a ton of useful info that may help you along the way.