It's possible that this is a deliberate application of GeoDNS, as many companies prefer that requests from, say, the UK resolve to a host located in the UK.
If you know that this is not the case, then you'll need to troubleshoot the resolution from each location. Old, crufty resolvers with hard-coded resolution paths for some domains, etc.
If you provide the domain name in question (it's public info, after all) you'll be much more likely to get a specific, useful answer.
There is something odd going on with your DNS. The .co.uk nameservers list two nameservers for your domain:
$ dig ns supadupawebdesign.co.uk @NS2.NIC.uk
supadupawebdesign.co.uk. 172800 IN NS cl4.owphosting.com.
supadupawebdesign.co.uk. 172800 IN NS cl3.owphosting.com.
But those two nameservers seem to be a bit... confused:
$ dig a supadupawebdesign.co.uk @cl3.owphosting.com.
supadupawebdesign.co.uk. 14400 IN A 126.96.36.199
supadupawebdesign.co.uk. 86400 IN NS ns870.websitewelcome.com.
supadupawebdesign.co.uk. 86400 IN NS ns869.websitewelcome.com.
$ dig a supadupawebdesign.co.uk @cl4.owphosting.com.
. 518400 IN NS B.ROOT-SERVERS.NET.
. 518400 IN NS C.ROOT-SERVERS.NET.
. 518400 IN NS D.ROOT-SERVERS.NET.
. 518400 IN NS E.ROOT-SERVERS.NET.
. 518400 IN NS F.ROOT-SERVERS.NET.
. 518400 IN NS G.ROOT-SERVERS.NET.
. 518400 IN NS H.ROOT-SERVERS.NET.
. 518400 IN NS I.ROOT-SERVERS.NET.
. 518400 IN NS J.ROOT-SERVERS.NET.
. 518400 IN NS K.ROOT-SERVERS.NET.
. 518400 IN NS L.ROOT-SERVERS.NET.
. 518400 IN NS M.ROOT-SERVERS.NET.
. 518400 IN NS A.ROOT-SERVERS.NET.
The expected result from either query would have been either NXDOMAIN (if I was requesting a subdomain that didn't exist) or a series of A or CNAME records. It appears that
c13 is trying to return an authoritative result and, at the same time, delegate the domain elsewhere. That could produce inconsistent results. And the
c14 server appears to know nothing about your domain at all but, instead of returning NXDOMAIN it's pointing me back at the root servers. Fortunately most resolvers are smart enough to avoid going into a loop at this point.
I don't see anything that would indicate why you might get different IPs back when resolving from different parts of the world, but I could certainly see why this domain might behave inconsistently. You can probably fix the
c13 results (eliminating the delegation) by editing your DNS config in whatever control panel they provide. You'll need to talk to your hosting provider's support department about figuring out if you need to change your NS records at your registrar to point to something other than
c14 or if they just need to fix
c14 so it has a valid answer for your domain.