I'm after some decent maps of a largeish area, the problem is it covers several areas of OS maps due to the area I need, so rather than buying 3 or 4 maos and sticking them together, is there any software or an online source of maps that would do the job. looking at the OS Explorer scale or similar.

look at Quo by Mapyx.

Although i fyou need to print out you'll be limited to your own printing capacity (unless youve got access to an A1 plotter or something)

you can order centred OS landranger maps, but they're limited in size I think. Look at http://www.mapsnmc.co.uk/osselect.htm as well.

http://wtp2.appspot.com/

You can get free OS maps here, I print screen then stitch pages together in photoshop for printing

You want an OS Select Explorer : 20km by 20km at 1:25000, centred wherever you like.
£17 from http://leisure.ordnancesurvey.co.uk/osselect

Just tried the OS custom explorer and looks like the area I need won't fit in the 20×20 limit. 🙁

Well the 20x20km at 1:25000 works out at 80x80cm – I guess that is the size of the printer for their custom maps.

You could go to Landranger scale (1:50000) or just order two customs.