There shouldn’t be any reason why that is the case unless it’s just poor policy on their part.
If you do then your site will be unreachable by anyone using a resolver validating DNSSEC (including most public DNS resolvers such as Cloudflare 1.1.1.1, Google 8.8.8.8, Quad 9.9.9.9 etc) until the DS records are updated by Fasthosts to those given by Cloudflare so check they will at least do that.
If they refuse, your safest option to avoid downtime is probably to disable DNSSEC for now and later transfer the domain registration to another registrar if DNSSEC is important to you. Although I’ve not seen this issue, other users of Fasthosts seem to have resolved their DNSSEC issues according to a quick search.
Hi I tried with it enabled but as you say when i tried to fetch page with google webmaster tools or bing it got unreachable despite nameservers propagating. Would I be better transferring to cloudflare the registrant if so how long does that take?
I am now being told “Hello, Paul. Apologies but we do not support DNSSEC within Fasthosts” So any reason why once i got confirmation email Cloudflare was looking after my site nothing could access it, bing, google etc?
You said DNSSEC was enabled. If so and you changed the nameservers, any DNS lookup through a resolver that checks DNSSEC will fail, that’s what DNSSEC does.