I typed "all of the below" before going on an INTENSIVE internet search. Apparently these jars are VERY hard to find in the UK, but I found you some :)
Here's links:
http://www.justpreserving.co.uk/advanced_search_result.php?keywords=home+disc...
http://www.cookability.biz/home-discovery-preserving-jars/b_697.htm
Search tip: I used Google advanced, and type in 'canning jars' as the phrase. Then used UK or Britain or England in the "or" section. That took me to several forum where people were helping each other find them. Apparently these jars are VERY difficult to find in the UK. Here's the results of that search if you want to look for other sellers:
http://tinyurl.com/create.php
(Here's what I typed before I searched)
Emmah, you're looking for the same jar that people preserve (generally via a pressure cooker) produce out of their gardens...like green beans, beets, etc.
Like 'wings said, you can use ANY kind of a jar with a lid that seals TIGHTLY (allowing in ZERO air), but if you're thinking about freezing them, you MUST have the jar that have the two part lids...when the juice expands (as it freezes), the lid on the top will "bow" upwards. The will prevent the jar from breaking in the freezer.
Maybe more pix will help you find them (???)
The "lids" are in two parts. A round, flat metal top (that is rimmed with rubber to make a seal), that fits atop the jar - and a metal band that screws around the jar and secures the lid:
The jars have a 'screw top' ridge - the flat lids are laid atop the jar, and the metal band fits onto the 'screw ridges' of the glass jar to tighten the band and secure.
This type of jar HAS to be used for preserving foods in a pressure cooker...but it does NOT have to be used for preserving jams, jellies, many pickles (or other things in vinegar).
Blessings,
Unyquity