First of all, what you have is not a true lemon but a hybrid between a kumquat (Fortunella) and a lemon (Citrus limon). I haven't yet managed to find out whether this is a new hybrid or an old one that is now being sold under the name 'Vulcan'. It seems to be being sold widely in eastern Europe but may be being grown by Dutch nurseries. Cirofortunella has traditionally been known as limequat/orangequat/lemonquat etc.
These ornamental potted plants are not really grown on dwarfing rootstocks, but on any available rootstock that is easy to propagate quickly. In fact (if they are actually grafted rather than rooted cuttings) they are grafted onto cuttings which are themselves rooted at the same time in a warm mist propagating system. Meyer's lemon is often used as a rootstock because it is very easy to root. The traditional way of producing citrus trees is to graft onto seedlings, but this takes longer - and the specific rootstock requirements for commercial citrus production do not apply to potted ornamentals. So, I repeat, the rootstock is chosen solely for ease of production. The kumquat hybrids are naturally fairly dwarf, and growing in a pot controls the size anyway.
You can grow more rootstocks from your seeds, but you can also use any other citrus seeds, or you can try and root cuttings from your original rootstocks - just as the originating nursery did.
Most of the information you will find about citrus rootstocks applies to maximising commercial fruit production, and is quite irrelevant to growing potted citrus in the UK.

Here is a link that might be useful: My citrus website.

Wow that's very interesting, so it's basically a cheap rootstock or maybe even the nurseries own rootstock? And my plants will only be dwarfed by pruning and pot size?

As for growing my own would I be better purchasing seed of this flying dragon. Seed (can't remember the proper name) for use on any trees I'd like to propagate?

so it's basically a cheap rootstock or maybe even the nurseries own rootstock? Yes.
my plants will only be dwarfed by pruning and pot size? And by the actual variety being naturally small, and by the fact that the UK climate limits growth. Unless you are growing a particularly vigorous species such as grapefruit or pummelo, you're more likely to have problems with lack of growth rather than too much!
As for growing my own would I be better purchasing seed of this flying dragon 'Flying Dragon' is the dwarf form of Poncirus trifoliata. The dwarf form is not needed in UK. Standard form of Poncirus trifoliata is a good choice because it is fairly resistant to root rots which can easily occur in over-watered, cool conditions. However, it is quite slow growing and in the UK will take at least 2-3 years to produce a grafting-sized seedling. Other citrus seedlings - lemons/oranges/grapefruits - may grow to grafting size faster and are perfectly OK for rootstocks in pots except for the problem of greater susceptibility to root-rots (phytophthera).
If you are interested in growing Poncirus trifoliata, I have seeds and seedlings available if you e-mail me.

Hmm I would probably be interested in seed or even seedlings (though I'm in no rush) but it will be later in the year before I can make any purchases.

Thanks
Nick