Pre-dreadnoughts would be mechanically unreliable for escort duty, and they were exceptionally vulnerable to torpedo attack, so I'm guessing the wear of constant duty would be brutal on availability rates, but theoretically if the British were willing to strip the Channel of its defences then they could form some pre-dreadnought squadrons capable of escorting convoys in the Approaches, and maybe one periodically off New York. The number of pre-dreadnoughts per convoy would be crucial, since against 1 BC raider as few as 2 pre-dreadnoughts might do, but against 4 BC raiders two pre-dreadnoughts would be sunk and the convoy still rolled up.
1 predreadnought per BC raider would probably be enough to deter the BC raider as the escort does not need to get a hard kill, it just needs to do three things.
a) Get off an accurate sighting report
b) Keep the raider occupied for most of the convoy to disperse ( a few ships will be run down but that is okay)
c) Credibly threaten to cause enough damage to the raider so as to allow the fast response forces to run the raider down
Sure this is rough on the escort, it is rough on the convoy but it works. The RN had 37+ predreadnoughts (Majestic to King Edward VII classes) where they would be very happy to trade 1:1 for modern German battlecruisers as the raiders get chased down by modern cruisers/battlecruisers once the damaged raider has a solid position fix.
And if the raiders are concentrating 4 or 6 BCs that is still a win as the problem is detecting the convoy. Keeping 4 raiders fairly tight covering a 50 mile search line means a lot of convoys get through cleanly without ever being detected. Unless those raiders are operating near convergence points (say the Bristol Channel, entrance to the northern part of the Irish Sea, Dover/Calais, Thames Estuary, approaches to St. Johns or approaches to New York Harbor etc, there is not a lot of traffic to find if most of the blue water merchies are being convoyed in fairly large convoys. Sure, this imposes a significant convoy cargo tonnage tax due to inefficient delivery streams to the ports but it is rough on the raiders.
Assuming the Germans can keep one in three battlecruisers in Great Waters due to need for training/rest/overhauls, they simply don't have enough detection platforms to both mob a modest escort of obsolete pre-dreadnoughts AND find a lot of convoys. The places where they can find lots of convoys are well watched waters near to British fleet bases that can dispatch heavy covering and hunting squadrons.