They are 'follow me' numbers which can be redirected to a phone anywhere in the world. These 070 numbers are commonly used by scammers who want it to look like they are in a certain country (in this case the UK) when they are in fact elsewhere, usually places like Nigeria.
+447024091560 is used in this scam. The travel agency, Global Travel Agency and UK Travels Agency is used in numerous fake job scams.
The scam is to get you to pay out for visa documentation which you have no chance of receiving..
Do not respond to them - you will be put on a 'mugs list' and your details sold to other criminals.
Do not send them money - You will be helping to fund criminals and possibly terrorists.
Do not send money via Western Union to anyone you don't know personally. No real company would ask you to transfer money in this way. It's untraceable and irretrievable.
Do not give them any personal details - beware of identity theft or bank fraud. Your identity may also be used to commit further crimes against innocent people and this could cause you serious problems in the future.
Please let as many friends and colleagues as you can know about this and ask them to also pass it on. Knowledge is the only way to stop these criminals