Don't worry, it's not rude to ask!
Breeding is just very risky. As lilspaz said, without knowing the entire lineage of your pets, as in their genetics going back multiple generations(what are your dumbo's parents like? his grandparents? great grandparents? do you know of his siblings?), you can really be getting yourself into a lot of trouble. There are a lot of very terrible, genetic problems with rats- such as megacolon found in high white genetics, or cancers, tumors, respiratory issues, and more.
I know you want to give your rats the best life possible, but, what if you breed a litter of rats that are all high white and all develop megacolon, which is a terrible, but common, disorder that results in weeks of prolonged suffering and eventually death?
Furthermore, if rats are not common where you live, then surely veterinarians in your area are not knowledgeable about them. What happens if your pregnant female has a problem during birth, and needs emergency surgery at 3am to remove a stuck pup or litter? If she doesn't get that vet care, both she an all 5 or 10 or 15 of her babies will die. Is that really the "best life possible?"
What if your rat has 10 or 15 babies? There is no saying you will be able to adopt out all or even some of them. Can you provide food, shelter, care, and medical care for 17 or more animals? Keep in mind, the typical vet visit for a rat, which is considered exotic, is around $75+supplies, medicine, surgery, any treatment, any procedure, etc.
Additionally, there are rats all over the world that need new homes, even, yes, in the UK. Here is a link to our forum for international rescues or rats needing home. Have a scroll through, and see that almost every other listing is for rats in the UK:
http://www.ratshackforum.com/forum/forumdisplay.php?f=21
Please do not think that with this post I am attacking you, or not trusting your knowledge or intention with these pets. On the rat shack, no one breeds rats, because those points apply to everyone.