Check this out
http://www.wikihow.com/Grow-Bamboo-from-Seed
In addition to those instructions, in UK I would suggest using a one of those electric propagators that provide bottom heat, as otherwise it often isn't warm enough here to get them going easily.

People generally don't bother trying to grow Moso in the UK. It is quite hardy enough to survive, but it doesn't grow well. It needs those hot sticky wet summers they get in places like Japan and much of the USA.

If your aim is to grow a big fat bamboo in the UK perhaps try one of the following and feed and water them very well, [and plant them well inside your property boundary, where you can mow all around it to restrict any escapes, or else install an effective rhizome barrier]. (all Phyllostachys species):

P. vivax: the species (green) or very common aureocaulis (yellow with green stripes) is fine, but hard-to-find huavenzhu inversa (similar to aureocaulis) is supposed to be best. Vivax aureocaulis is sold by some non-specialist garden centres, but you'll probably pay less by getting it from a bamboo specialist.
P. "Shanghai 3": fairly widely available from exotics specialists, green, not so different from vivax (species)
P. atrovaginata: hard to find, but the fattest bamboo they have at Kew
P. irridescens: another rare sought after one

there are also some rare and special ones like Chusquea gigantea, that you would have to pay a lot of money for.

People generally don't bother growing from seed either, for a number of reasons:
- Most species there is no seed available, because they hardly ever flower
- A lot of species the seed needs to be very fresh to be viable, so a lot of people buy dead seed from unscrupulous internet sellers and get nothing
- The bamboo grows very slowly at first, and will take several years to reach the size of what you can get in a 5-litre pot from a garden centre - there is a reason those 5-litre pots cost 15 to 30 pounds or more, depending on the species.