Problems dialling an +448xx/+4470x numbers from outside the UK are normally related to dialling the incorrect access code. When you dial any UK number, you must include all the international codes necessary for calling the UK. (always remove the first zero of UK numbers, when calling from an international phone line)
For more information on international access codes please click here
IMPORTANT: Ofcom the regulator of the UK telecom industry has requested that all international telecom operators make +448xx/+4470x UK numbers available from overseas phone lines. When a UK number is dialled from an international phone line, it is the originating call provider (OCP) in the country of origin who is responsible for routing the call to the UK. If your call cannot be connected, then you must report this fault to the originating call provider (OCP) being using to make the call and have calls to these UK numbers unblocked. OpenTelecom cannot be held responsible if certain overseas telecom operators do not permit access to these virtual UK numbers.