Most older frames had a distance of 120/125mm between the rear dropouts ( inside edges) They then have since moved out to 130mm to accomadate the latest hubs.
If your frame is an older cro-mo steel frame it is reasonably easy to adjust the rear dropouts apart.
Aluminium frames in the early days did have 125mm and are a little harder to ease out, as aluminium is not very flexible....but with a bit of power pulled apart.
A good bike shop should be able to do this for you
Thanks for your advice - sounds promising! I think its a CroMo frame but the chainstays are shiny (excuse my ignorance) polished metal - would that indicate alu?
Vitus frames were made in aluminium bonded onto internal lugs which give a seamless type finish.
They also were made in carbon fibre ( black tubes) The frames were made to various brand names.
With this type of construction it would pay to have the rear ends professionally eased apart. If it is forced crudely the bonding can be broken and will need reglueing ( araldite).
I am a Kiwi just returned to NZ after 4 years in the UK and Europe in the bike industry....its good to be home! just had an amazing summer here.