-
Bits of debris flying around in low earth orbit (where all the satellites are) smash into a satellite causing it to break apart, this leaves even more bits of debris flying around making further collisions more likely. Eventually (20-30 years they estimate unless something is done) it happens enough that all satellites in low earth orbit are obliterated and anything new put up there would be destroyed within days.
Even getting a new satellite (or any other space rocket) through the debris cloud at low earth orbit height would be risky, so space exploration gets put on hold for 50-60 years until it all smashes itself apart and the bits burn up or fly off into space never to come back.
But, most importantly...
No satellites means no GPS.
No GPS means no Satnav.
So suddenly knowing your way around London becomes a very valuable asset.
The Knowledge will become a lot more valuable in 20 years or so if nothing is done to prevent Kessler Syndrome.