Right it sounds like the machine has error code 11, which is a filling error.
The fact engineers have been out suggests this could also be a control board failure, since I would have expected the engineers to see error 11, look at the inlet valve test that is working and the hose isn't crushed\kinked.
Providing your sure the inlet hose is letting water to the machine, with the power switched off I would check the machine filter, drain any water which may have found itself inside previously, with the filter left open and a bowl\towel in place to capture any water, set the machine to a rinse programme (10 o'clock position), turn the power on and see if it will start, I would then power it off and try and set it to drain (one click anti clockwise) and see if that make the pump start, which you can see from the hole where the filter sits.
If these tests fail its a control board failure, which is £150 part so you need to get on to Zanussi.
Please let me know if you need anything clarified.
Error code 11, 11 flashes I dont believe to be a power fault.
If the washing light flashed 11 times this would signify error code category B, followed by the 1-3 flashes of end would give B1,B2 or B3. Since you state only End is flashing this is a error code category E, followed by 11 flashed of end gives E11.
This may be why the engineers have attended multiple times and not fixed the issue as they are thinking its a category B fault, it may well be where they have replaced the power regulator, cables etc they have disconnected the actuator for the inlet valve and generated another fault, however would have thought you would have noticed if it was flashing 3 times and now flashing 11 times after a visit.
In conclusion I think this is strongly looking like a control board failure, not a power failure, but certainly not something which can be fixed without stripping the unit down and checking all inputs and outputs with a multi-meter.
Yes this would have a significant impact, most UK washing machines work on 230V but can cope with 240, however it requires a steady voltage and current, most inverters voltages drop as you apply more current so you do not get a smooth AC sine wave, secondly you may find the inverter is not able to provide the required current. The website here explains the difference between mains and inverter AC generated power better than me. I am aware people who are off grid and use solar power have the same problem with a 'modified sine wave inverter', and the solution has always been to chose an old style machine with analogue programmer\timer etc. That said this should have been picked up by the engineers, they have equipment which can monitor the machine when under load and it should show either the voltage has dipped, the sine wave is irregular or insufficient current is provided.
I think you will struggle to get the manufacturer to agree liability if your using a inverter which doenst produce a smooth sine wave, having a look on forums this appears to be a common issue with the more recent washing machine models.
Sorry I couldnt offer a quick fix at your end, I would certainly speak to other owners to see what model they use, as it appears to be a trial and error, alternatively its a case of replacing the inverter to give you one with a smooth sine wave but thats a big expense to wash some clothes.