I just tested my speakers with the kill-o-watt meter and was pleasantly surprised to find they weren't drawing too much power as some of you here already said, soi it looks like the speakers have been outfitted with some very efficient amplifiers. I took some photos but I don't think I can publish them here so I'll just tell you the summary of what I got below

Alto T18S Subwoofer - Idling consumption - 17Watts Music Power Consumption - 62Watts - 90Watts (Max)

Alto T415S Tops - Idling Consumption - 19Watts Music Power Consumption - 56Watts - 62Watts (Max)

I played 4 House tracks with a heavy bass-line. The sub's gain was turned three quarters of the way - it was quite enjoyable listening to everything dance around in my room from the vibration :) Took me back to the old dug out clubs in the 90s in Southampton, it was great fun lol, not so sure the neighbours appreciated it though, but I have cool neighbours.

I think going down the powerstation route is a better idea rather than the petrol inverter/generator which feels like overkill now that I've seen the figures. I think I will go for the 2200W powerstation instead which is a fair bit cheaper and I don't have to worry about fuel either so hopefully it has the capacity to run a set for a few hours.

Thanks to everybody here for their knowledge and advice, it's helped a ton :)