VAT is hideously complicated. Archaic laws dating back to the 70s; EU directives and you’ll often find that, even if you do refer to the latest legislation (1994), it’s not very helpful.
This means that you need the help of people who know how precendents have been set and why they have been set.
The answer to the questions, “Can/should/must I register for VAT…? What can I claim for…?” are often a lot more complicated than they appear at first glance.