They shouldn't exist, but they do. C-roads, D-roads, U-roads and others can sometimes be found if you know where to look. Here's a set of photos showing that these things really do exist!
If you head south through Scunthorpe on the A159, you'll encounter this sign when you cross Station Road — the C173. Photo by John H Boddy
Just to double check it — yes, it's signed exactly the same from the other direction! Photo by John H Boddy
Signs ahead of this roundabout on the B1217, close to Scunthorpe, reveal you can find the C221 further down the road. If you continue in this direction there's no further mention of the C-road. Photo by John H Boddy
Another double check from another approach to the roundabout — yes, the C221's still there! Further along the B1217 there used to be signs denoting Scotter Road as the C221 but these have since been removed. Photo by John H Boddy
This one runs from Laurieston to Gatehouse of Fleet, and this photo proves its existence. Ladies and gents, the C13! Photo by E J Matthew
This (and the one above) are on a traffic island, but have been turned away from the road. Photo by Chris Larsen
The C137 also goes to the A167, so you have a choice of C-roads if you wish to go there. Photo by Chris Larsen
Looking at this bridge along the route, it's never going to be more than a C-road! It's two metres (6ft 6in) wide and signposted with a 10mph limit.
In Northern Ireland, travellers on the A20 near Newtownards are given the option of travelling on the C264. Photo by Wesley Johnston
Here's the other sign at that junction, visible in the background of the previous picture. Photo by Jonny boy
This charming example is north of Portsmouth in Horndean. (The sign is also wrong; its blue patch should read "(A3(M))"...) Photo by Deryn Hawkins
The C237 was hiding away in Poyle near Slough — but the sign's now been removed. Photo by Mark Stevens
The C368 has been tracked down at the northern end of the A19 at Seaton Burn... Photo by Toby Speight
If you head north you might like to visit the C3047 between Shap and Penrith, just off the A6... Photo by Dan Warrington
...and if you keep going that way you might end up at Tarbert, Kintyre, to see the UC26. Photo by Dan Warrington
If you spot the C1268 on a sign try not to panic, because it's only a typo for the B1268. Oops! Photo by Ken Coton
This self-important C32 sign is at Hawes in North Yorkshire — why is it yellow? (Geoff Eddy also sent in a photo at the same time, but it was pretty much the same and Colin won the coin toss. Sorry Geoff!) Photo by Colin
This pre-1963 example on Islay in the far north of Scotland was first spotted by Richard Smith, but it took the skill and cunning of Ben Harper to photograph it. Photo by Ben Harper
For a while the C100 made an appearance at Handy Cross, on a temporary sign as part of the now-complete motorway junction upgrade.
The C1146 is seen here in Ceredigion (or, if you're an old traditional Empire-building type, Cardiganshire). Photo by Jon Bentley
Careful. Innocent people minding their own business near Benbecula Airport, between North and South Uist, have been quite startled when this C-road suddenly appears. Photo by Mike Burns
Explorers may like to fight their way through the swamps and jungles of Lincolnshire to find the C326 on a venerable fingerpost in Caythorpe. Photo by Colin Ward
This C-road in Pembrokeshire is announced on a sign that was erected when the whole of this narrow track was widened, as part of a wind farm project. Photo by Ceridwen
The C13 (not the same as the one to Gatehouse of Fleet, above) was seen for a while on the Blandford Forum bypass. We can all relax now that we see access to the Sunrise Business Park was unaffected. Photo by David Brown
This sign for the C1 in Scotland was taken in August 1985. It's probably not there any more. Photo by David Harding
This sign in Surrey is so marvellously complex that it's easy to miss the erroneous appearance of a C-road number. Photo by Neill Wood
Here's a sign dating from the 1920s in Norfolk (or at least, made exactly to the early 1920s Ministry of Transport standards), showing the C83 near Middleton. Photo by Ben Harris
Here's a picture of the matching sign at the other end of the North Yorkshire C32. They make quite an odd pair. Photo by Rob Shufflebotham
The second part of a C83 double bill comes with this one near Solas in the Western Isles. Photo by Peter Asprey
Take a moment's break from conquering the Highlands to admire this sign for the C1050. Photo by Toby Speight
We've already met the C13 towards Gatehouse of Fleet. Turns out there's more than one sign for it. Photo by NDMcN
Lurking in the still darkness of the Lake District is the C2030, ready to frighten passers-by. Photo by Rob Shufflebotham
In North Yorkshire, travelling east from Stillington to Sheriff Hutton, a road closure outs this road as the C91. Photo by Andrew Straw
Moor Lane — a local road leading off the old A1 in North Yorkshire — sports a shiny new sign referring to a weight restriction further ahead, revealing that this is the C278. (It was also spotted and photographed by Jeremy Hunt.) Photo by Clive Jones
The C79 — which we've already seen, further up the list — has a sign at its opposite end which has a home-made reference to its number, seemingly made of stick-on letters from a DIY shop. Photo by Robin Horton