OK - here I can speak with some authority
All OS mapping is commercial product, so there is a problem off the bat with possible usage: if you want nto draw a map for others to follow, technically you need a licence from OS to use their products. OS maps at 1:10K & 1:250K are actually freely available, the rest cost money to acquire.
I'm not really sure what your intended usage is: are you wanting to plot a route so you can follow it later on (ie, self-navigation), or are you wanting to have a base map that you can produce a printed map with route & other details on it (like we do for stage maps in motorsport)?
Self-navigationIf its the former, then Fugawi UK and Memory Map UK will give you 1:50,000 maps that you can plot a route over, and then follow as you walk or drive. Another popular application in Anquet Maps: cheaper initial outlay, however you have to by individual maps, so it becomes more expensive as you want to cover more of the UK.
There are even various programs you can buy for smartphones - however I've not used them much, so can't comment on their ability to create pre-plotted routes.
Choosing between the three main applications is mainly a matter of personal preference.... and what your friends use
Making mapsIf, on the other hand, you are wanting to produce augmented maps, you are looking of .jpg files of maps: If the 1:10K & 1:250K maps are not want you want (see
http://www.ordnancesurvey.co.uk/products/os-streetview/index.html &
http://www.ordnancesurvey.co.uk/products/250k-raster/index.html respectively) then it becomes harder still.
If you are in Academia, then you may have access to Digimap (
http://digimap.edina.ac.uk/digimap/home) which allows you to download images.
What I've seen done is use the streetmap.co.uk and save the tiled images of OS map, and then stitch them back together in your favorite graphical image manipulation program.
Oh - and if you're going to go this route.... two things:
1) Fugawi UK for sure, and probably memory Map UK, cannot import maps - so they can't be used to follow the wonderful maps you have just produced, and
2) can I suggest that you create a base map, which you then copy to crete your stage maps on.... and you use a Graphic Image Manipulation Program that uses Layers so you don't actually draw on the base map (it will save you LOADS of grief later on)
..... but see my comment on copyright at the top