Michael - This mark is similar to a mark used by US potter Mary Law (see further down this list); the difference being, in Law's current mark the M and L are conjoined. I wonder if she changed it due to confusion with M. Leach. Law studied with Byron Temple (though I don't know if it was in the UK, or during his period in the US. You can Google her name + ceramics and find her website--you might contact her to check. She is currently working in Berkeley, California, USA. She has been around for some time and is currently finding some notice among US pottery fiends.
Mark Nuttall - confirmed by mary law this is not her pot still possible it is michael leach early vase as that is what it was purchased as