It sounds like you need a mechanic who is experieced in vehicle engines.

in fact whole purpose of my request in the forum is to get the opinion of technical experts before going to the same mechanic or a new one. Basically if the gasoline return line is getting pressurized is it normal and if not what could be the reason. Then I can be sure that the garage mechanics are not trying to take me for a ride

Two things make liquid flow. Gravity and pressure.

A car's fuel pump typically has the capacity to deliver more fuel than the engine can use. What is not used is routed back to the tank in the return line. Logically, both the line from the tank and returning to the tank are under some rated pressures, but to Lyn's point the latter should be much less and gravity is not going to get it there. Your mechanic should be able to reference the manufacturer's specifications for fuel line pressures and check to make sure your car is functioning to those specifications.

It sounds like a blockage in the line at the tank end

that is exactly what we thought. I took the car to the garage and checked the line at the tank end. The flow was good and car is now deemed to operate normal. I will monitor fuel consumption and report on outcome for the benefit of others on a latter date