Yoyo: I'm sorry that we've not yet had any responses to your uniquely-shaped Dragonfly but, hang in there, this is PPRuNe and strange things can (and do) happen!
The number of those still 'kicking' with hands-on experience of this type are few and those with such experience who venture online even fewer!
We could embark upon some research ourselves if there were a serial number or registration to track but, alas, we are not given this information. There is obviously a story behind it (perhaps an experimental development by Westland prior to homing-in on the Widgeon?).
More 710 ..
710 at a 'Salute to the 40's' open day at Chatham Dockyard