do you have any kind of OBD2 adapter (wi-fi, BT, USB) so you can use some software on your smartphone (torque, Car gauge pro, FORScan Lite) or your PC (FORScan) to check the problem?
that's the first step IMO.
you can get cheap OBD2 adapters of ebay for a few quid.
I even manages to clear the code using this cheap one what I was afraid I wont be able to do cos these are cheap Chinese clones of the devices so sometimes they lack options.
edit: how many km you have on your car? As I understand original lambda part (2nd one), which is BTW Bosch part No. 0 258 006 713, and you can get it directly from Bosch or auto part stores for 2-3 cheaper than in Ford shops, should go for at least 150 000km.
this is my original lambda probe (2nd one, after the CAT, called post-cat or downline if I'm not mistaken):