Hi, it's a steep learning curve - I hope you're ok.
My daughter who is now 14 had ABA from the ages of 3-10. Some LAs will fund ABA without a fight but ours isn't one of them and we got ABA via a tribunal order. If you want to know anything about providers, feel free to pm me.
Yes, ABA is available in the UK but you will need to be able to fund it yourself at least to start with. If you meet their criteria then you may be able to get a grant from a charity called Caudwell.
If you do a mumsnet search then there will be loads of old threads regarding ABA. It may also be worthwhile having a look at the ABA yahoo group and the ABA4All Facebook page.
A great book to read as an introduction to ABA is by Robert Schramm called 'Motivation and Reinforcement'.
You can find ABA consultants on the BCBA website. If you are lucky enough to have the choice of several (you may not depending on your location) ask lots of questions and speak to the families they work with.
to get it funded you have to apply to the council for education, health and care plan (see IPSEA website) and ask for ABA to be funded as the placement (although its also poss have 2 placements e.g. ABA + a school). Most councils don't want to fund it as generally its more expensive than their local special schools or mainstream provision. If the council refuses you have to go to tribunal and ask the tribunal to overrule the council's decision. My council only funds with a tribunal order. if you get a EHC Plan you can ask for a personal budget and some councils will agree to you using the budget of their own provision would cost towards ABA.
In UK ABA is treated as education provision - whereas in other countries its covered by health insurance
We won our tribunal and although it was hard work and took a long time to get that far my son has now had 6 years of ABA funded (35 hours a week, 48 weeks a year) which has made a huge difference to him (and us) and it was worth fighting to get it. We had to prove the local options could not meet his needs - we did that by sending him part-time to the local nursery with speech therapy and autism outreach the council / NHS provided and proving that he made no progress with that - we did ABA privately at home PT and showed that did lead to lots of progress.