That's the stuff Jeff, i bought the reel then had second thoughts so returned it and had a refund. Started again at the wholesalers with their top man. Explained the power of the vac and everything - his reply was "sorry we are not allowed to advise".
So, came back home and sent a text to an electrician i know who said exactly the same as you Jeff - Artic cable with those special type connectors 'cos the cable won't fit in your normal plugs. So now i'm confused because Alex has posted a normal extension lead?
The special plugs your friend is saying about are the 110v type,(round in shape) is your vac 110v or 240v?
If its a 110v then the above plugs apply, if its 240v then the standard plug will fit, but for your added safety fit an RCD device, any fault with the custy's electric or your vac won't come back and bite you on the arse
Also if H&S walk around the corner he may just let you get away with it with the RCD fitted, as all external work with electric should now be in 110v.
The artic cable will fit into the standard plug with a little help, its the correct cable for external use and as the name suggests it can be used in freezing conditions, its Hi-vis, and most important its heavy duty, so ideal for your needs.
Most electrical out-lets are not allowed to give any electrical advice unless there a qualified sparky and even then a company may not allow it, its all down to IEE regs.