Volvo V40 no power from ignition

I bought this Volvo car 3 and a half years ago. I understand that it is fitted with a Mitsubishi engine.
Last Monday as I was driving along approaching a T junction I slowed down to stop. The car seemed to cut out on me. I thought that perhaps I had stalled the engine. When I tried to start it up again there was nothing from the ignition switch when turned on. No dashboard lights, radio or headlights came on when key turned to On position. Everything else such as cigarette lighter, horn, interior lights and parking lights worked OK. So I knew it wouldn't be the battery. All fuses seemed OK. I was able to tow it to the nearest garage which was about 100yds away. It's been there for 5 days now and the mechanic there can't tell me what's wrong. Can you advise at all?