How do covert a grid reference into a Lat and long?

Question

The GRID REF IS OS MAP 177 Grid Ref 386 780 and location is near Greenwich University.

Answer 1

What a confusing system!

This is entirely a guess.

I did a websearch to find what "two-letter" code corresponds to OS Map 177. I think it's going to be TQ.

I then found a conversion program here:

http://www.russ-hore.co.uk/osgb/index.php

So I typed in tq386780 (not even sure if that's right! the number that I replaced was 4 digits longer...perhaps that's because it was more exact?)

Anyway the answer I was given was:

latitude = 51º 29' 00.47"
longitude = 000º 00' 13.33"

Which is pretty close to longitude 0º, so I'm confident it's near Greenwich longitudinally at least.

If this is not right, sorry, I tried my best.

I would think that the Ordnance Survey would have this on their website somewhere (not to mention something to convert from OS Map to whatever those 2-letter codes are).