Got out for the day on Friday. Wore the ultra expensive Simms wading belt. It fastens at the front and then there is adjustment at the back. Took a few shots to get it on and then be able to get it really tight. However it is very supportive. It really held my lower back in the correct position. As mentioned by mark it adjusts very easily so could slacken it off to sit down and then tighten it up after lunch.
So all indications suggest that the £90 was worth it!