5 amp plug

How many of these did we throw away in the UK, converting from round pin 5 and 15 amp sockets* to the current standard of 13 amp square pin sockets?

We found a couple of round pin sockets in our lounge, in our modern (built in 2005) house.  I was confused, but Mr Google revealed that these were probably on the lighting circuit, which explained the light switch that didn't seem to have a function.

Had to buy 5 amp plugs!  Now replugged the new (to us) standard lamp, and it works as expected.

*most of the sockets in my childhood home were round pin.