Disaster averted on the 'Needle Bar Thread Guide' front folks - yay!
As I should of known the lovely and most helpful Helen Howes had a suitable replacement part over to me in a lickety-split, and best of all it only cost me £1.00 + the P&P ... what's not to love? I bought an extra thread guide (another £1), and a spare presser-foot (£2.50) too - all pre-loved items now finding a new lease of life with my sewing machine :)
BTW I did find the broken piece from the original guide - it somehow landed onto the set of drawers directly beneath the table the sewing machine sits on - v. clever considering the drawers are about 2 ft to the right of the machine and sit flush with the front of table LOL!
The replacement is from a different make and model of sewing machine, but having seen it's photo on her website I was pretty confident it would fit and it does :)