obviously had not done enough research before posting! The solution that worked for me was:-
1. Clear my kindle of all existing books / collections (my choice to do this
2. Tag the books that I wanted to send as collections using 'Edit metadata in bulk'
3. Create a virtual library using button towards top left based on Tag created in 2
4. Select this 'Virtual Library' (highlight all) and send to device
5. Use 'kindle collections' to create the collections on the device.
Not sure if I have remembered all the steps exactly but it is a relatively painless process.
Apologies to those who kindly replied -- should have spent more time with google and less time playing around in Calibre