And it makes perfect sense from the Brits' perspective, as they would like to avoid a nonstop TLV-LHR-TLV itinerary to be cheaper (tax-wise) than a TLV-FRA-LHR-FRA-TLV itinerary.

So, in order to avoid the higher longhaul tax, it would be necessary to buy two seperate tickets: one TLV-FRA-TLV and one nested FRA-LHR-FRA. Of course, the overall price of such a construction might be just as high or even higher than the standard option. Not to mention potential problems in case of irrops.

Why did the Brits establish the extra "tax"? I reckon it is to fund the extra security harassment and humiliaton pax going from, to or through the U.K. are entitled to these days.