We are the Travelling people like the Picts and Beaker Folk,
The men in Whitehall think we're parasites, but 'Tinker' is the name.

All the jobs in the world we have done
From making Pharaoh's coffins, to building Birmingham

That's a very Kiplingesque reading of history, Jim - almost plagiarism! Heady maybe, but historically wayward too; both The Picts and The Beaker Folk were very much the unitary authorities of their time. In the case of the latter their dominion extended throughout most of the British Isles and was powerful enough to marshal the forces that built Silbury Hill or else drag the blue stones from Preseli Mountains to Salisbury Plain.

Slave labour? That's too simple a reading. Even your pal Ewan MacColl celebrated such municipal engineering projects as a source of proletarian pride, as he did here in his song abut the building of Blyth Power Station:

Blyth Power Station Record Breaker Part 1 (from 1.30)

As for Pharaoh's coffins - the techniques of their construction might baffle the most eminent of archaeologists today so I don't think we're talking itinerant labour here somehow...