To find a date you'll need to look at how the letter 'R' appears. e.g. is it within a shield, an octagon or whatever? Take a look here to compare your mark with the official list:
http://www.theassayoffice.co.uk/date_letters.html
(NB: You'll probably need to press Ctrl and + together a few times to make the page easier to view comfortably. Press Ctrl and 0 together to return to the default size).
The most authoritative online listing of makers' marks I know of is here:
http://www.silvercollection.it/hallmarks.html
'MHR' isn't listed but there are photographs available within the 'Images' sections, so you can look for something similar.