I don't think you have enough information to complete the analysis you are attempting to complete.
First of all, electrical loads are measured in amps, not volts, since your AC voltage will remain (in theory) constant when plugged in. If the tech meant to say 3.8 Amps or Amp-hours, then we could complete the math. IIRC, UK operates on 240 volt system (50hz doesn't matter when calculating power draw). 3.8 Amps at 240 volts is 912 watts, which for an hour would be 912 watt-hours or .912 kWh (kiloWatt-hours).
Btus are just another form of energy measurement, so if we convert kWh to Btus we find that the electrical heater is using 3112 Btus per hour (1 kWh = 3412 Btus), compared to the estimated 2300 Btus per hour on propane. As mentioned, the propane will yield about 80% of its heat in a refer application (minimum 20% heat loss), which would net out to 1840 Btus per hour used by the absorption chiller. Obviously, something doesn't quite add up between the propane and electric values you were provided by the manufacturer, since the energy actually used by the unit should be equivalent.
Second, I believe the tech may have provided you with capacity numbers. In other words, how much "can" the refrigerator use in an hour. The actual usage will be dictated by many factors including external temperature, internal rig temperature, refrigerator cold setting, how much warm food you just put in it, etc. I suspect your actual usage will be much less than the values provided by the manufacturer.
Think of it this way...if the estimates provided to you were accurate, you would be losing the amount of heat equivalent to running a 900 watt heater.
Another "gut check" comparison, would be to consider a household refrigerator (different design and thermal cycle I know), but an average residential style refrigerator will use 700 kWH per year. If your RV unit were to run all year at the suggested wattage given to you, it would use 7,989 kWh per year. Again, something seems amiss in the numbers you were given.
Assuming the values were correct, the analysis would be as follows:
Btus Gas = 2300 / 24,170Btu per L x 0.37quid x 8,760 hours per year = 308.43 quid/year
kWh Electric = .912 kW per hour x .17 quid per kWh x 8760 hours per year = 1358.15 quid/year
The reason electricity is typically more expensive on a Btu basis is that you lose approximately 65% of the energy in fuel when it is converted to electrical energy. This means, to make heat, burning fuel at the source is MUCH more efficient than burning fuel to make electricity and using that electricity to make heat. It's not that simple of course, but you get the gist.