Thanks for the link adpawl I will have a read through that.
Did a full virus/malware/spyware scan on both PC and Laptop, both are clean. No problems there.
I did another test this morning. I made a note of my IP address, went on my site and the spam was there as expected.
I restarted my router so I could obtain a new IP address. I then went back on to my website and the spam was gone.
So it’s definitely something to do with recognising IP addresses