Up to 2018 (and hopefully beyond), the Streetmap website displays OS maps without a subscription, and allows you to search directly on grid references. To display a map via Streetmap needs three parameters - eastings, northings, zoom level. 

In our part of Britain, grid references begin SP, the eastings begin with a 4, and the northings begin with a 2. 
Zoom level "120" corresponds to the Ordnance Survey 1:50,000 map series.

So, to display a map in the Streetmap website for SP222333, you need a hyperlink reference like this:

                     http://streetmap.co.uk/grid/422250,233350,120

For more information about linking to Streetmap, see http://www.streetmap.co.uk/idlinkto.htm