The Lat/Long out of the AIP will be in WGS84 format (World Geodetic Survey, if you want to know). Everything and everywhere has had to be resurveyed over the last few years, prior to that it was OSGB36. WGS84 is always in deg/min/sec even though the figures are altogether, so 513434 is 51deg 34min 34sec.
It looks like 51.3434 has been accepted by Mapblast as 51 *point* 3434. If you click on it in Mapblast it converts to deg/min/sec and comes back as 51deg 20min 36sec and therefore not where you think it is.
OSGB36 from the AIP where in the form deg/min/decimals of sec. Note that OSGB36 and WGS84 are not the same. Everything (in the UK) 'moved' between 20 and 200 metres north west!!