I spoke to the ISP. The rep started off by saying I shouldn't expect more than a couple of Mbit upload speed, and explained at length that upload speed depends on the server that's being uploaded to!
That didn't wash with me and I pointed out that the EE advertising states 11-20 MBit. So then the rep went into my router and showed me the upload speed that the router displays. I couldn't see a way to argue with that!
Maybe there's more to this. But I don't know where to start, really.

Thanks very much for your comments, though.

This is ongoing. I spoke to a university network manager who pointed out that the router shows the sync speed, which indicates the maximum speed attainable. But the real speed is normally below that. And in my case the ratio is consistently 80:2. So now I'm in the middle of a formal complaint with EE.
One of their CS representatives did at last acknowledge that download:upload should be in the ratio 80:20, so perhaps I'm making progress!
I hope this info - that the sync speed is not necessarily the connection speed - is helpful.

The 2 speeds are measures of 2 diff but related things.

Sync speed is the actual speed of the connection which is carrying both your data + protocol overheads for routing the data, It is normally measured in bits/sec. This is the speed that ISPs quote.

The throughput from this (what you call the normal speed) measures the speed of the data alone w/out the routing overheads and so will be be less than the sync speed. It is normally measured in Bytes/sec.

On ADSL throughput is usually about 83% of Sync. On Fibre it is considerably higher; about 92% of Sync.