I believe the best way to stop sea lion as a UK player is to buy an AB and either all inf or 1 inf and 1 fighter. Assuming no J1 (because if this happens it is a very good sign sea lion is off the table) the only combat I suggest is attacking sz96, cleaning up the Atlantic ocean of subs in sz 106 and attacking the German BB if it is in a vulnerable spot. Depending on the bid the attacks generally look like a sub, tac from 98 and fighter from malta for sz96. Destroyer from sz109 and maybe bomber to attack any subs in sz106. And depending on where the BB is use fighters unless it has retreated to sz112.
For non-com movement I move any ship that can reach to sz 92 while picking up the inf and AA in Malta and unloading in Gibraltar. I make sure I land at least 2 fighter in Gib and the rest in London. With the navy parked there it makes sea lion all but impossible while still preserving the majority of your fleet. I also move all land units in Africa back to Egypt (not sure this is the best idea but this is what I prefer) and use the transport in sz39 to activate Persia.
A smart axis player will realize sea lion is now off the table and move towards Russia. An even smarter Axis player will realize this move all but takes Egypt as well if the US buys any transports for the east coast early (this is just an opinion).
Saving the air force is critical for this move so I rarely scramble in sz110 and will think hard about scrambling sz111. Unless the German player buys all land units R1 and Japan attacks as well this tends to be my opening for UK since it does a great job of securing the strategic objectives that were mentioned earlier in this post. If the party gets started early I might get more aggressive and attack sz97.
I do not like to trade the UK navy plus planes for the Italian navy considering that if I can trap it in the Med, the Italian navy is strategically worthless outside of defending against an amphib assault. Plus any inf bought for London are strategically worthless until mid game at the earliest.
When you crunch the numbers the end result is a force in sz92 that should easily withstand everything the Italians can throw at it. Also every unit in sz92 and on Gib can now be used to defend London if need be.