I use a camelback rather than a belt. Amazed how comfortable and light it is and I really don’t notice it while running. Best thing is it’s so easy to take sips from as you go. Cotswold Camping on Western Rd have a good selection. Evans Cycles was also good but they seem to generally be carrying lower stocks of everything now.
Sweatshop usually have Shotblocks - personally I like these long with Gu gels but it’s definitely down to personal preference.
Ditched Camelbak a long time ago.......contents heat up way too quickly......waist belt with 2-3 300ml bottles for me