Update 2014-09-07 I've just ran a workshop based on the Astun Leaflet & and ol3 examples at OSGIS 2014, see Practical OpenLayers 3 & Leaflet for details.
Update 2014-05-15 For examples of displaying a Web Map Service (WMS) layer in a custom projection (EPSG:27700) within Leaflet and OpenLayers 3 (ol3) see …