[Jim Reid]

You *still* didn't provide enough information. What are the resolver
settings on the system that's performing the lookups? And what is the
name being looked up?

The zone file you showed is syntactically OK, but doesn't tell us what
name you were trying to look up.

Oh and according to the internet, the a1ms.co.uk zone appears to be
administered by netbenefit.co.uk and is served by their name servers,
ns0.netbenefit.co.uk and ns1.netbenefit.co.uk. Mail for this domain is
delivered to mail.a1ms.co.uk, 194.129.145.50. All of this information
directly contradicts what's in the zone file you showed. And your zone
file claims that ns0.pipex.com and ns1.pipex.com serve a1ms.co.uk. 
They don't. Why are you configuring your name server to impersonate
somebody else's DNS zone? Maybe you would be better to start at the
beginning instead of making your name server tell lies and then trying
to figure out why it doesn't work the way you want.