Unfortunately this post won’t live up to any expectation from it’s title and has just turned in some links rather than my intended musings.
wheresthe Path? – can bring up Google Sat view from British National Grid tile ref e.g. SE1234
Street Map includes 1:50,000 & 1:25,000 OS maps and accept British National Grid ref e.g. SE1234
Open Street Map – maps you can contribute to!