I'm not long off getting my 125cc Motorbike, it goes about 49mph. Is this okay for the motorway (not long journeys).?

Other answer:

125 doing 49mph? is it a 'dual sport' Trial or trail model with low gearing? Some kind of 'colonial' tuned low octane gasoline burner? MPH instead of KPH implies maybe US instead of UK or EU–what is the Actual motorbike? -something from mainland China or a 'Classic' with a Villiers engine about 5hp? – or something with a ignition or throttle restriction? Motorway implies UK/British poster and even the older restricted 125s had 10 to 14.5 hp or whatever the KW conversion was- and that meant good tuned engine did 65mph- what I got out of 100cc Honda fixed for girlfriend at the time. Indicated 75 mph, traffic on road doing 65 limit behind police car or so and speedometer checked at with pace car that had recently tested speedometer. I cruised that little critter at 55 to 60 on roads with 55 mph speed limit at 1500rpm under red line for 15 to 20mile trips to work and family homes. In US the 125cc isn't legal for main federal interstate system (need 151cc), fine for most state roads, county roads.
You need to specify in which country you plan to ride your motorbike? Most 125cc machines should be capable of about 60mph, which would be OK for short journeys on UK motorways. 49mph would be too slow to be safe, because all the traffic coming up behind you would be doing 60-90mph: trucks, buses, cars, regardless of the speed limit. No, you cannot ride slowly on the hard shoulder / breakdown lane, because that's not continuous and it's only for breakdowns.
If you only have a provisional Category A licence and 'L' plates, it is illegal for you to ride on a motorway, anyway.

Even if you have a full licence, a bike that is only capable of 49mph will be a death-trap on motorways, as everything else will be going faster than you. Everything…

You are not legally allowed to ride on motorways with a CBT. Plus, 49 mph is no where near fast enough to not cause problems on a motorway.
Anyway, a 125 should be able to get up to at least 60 mph!
I would watch this video showing the good and bad about motorways and low powered bikes
Timbo is here:
If you mean the UK then no 49mph is not fast enough for Motorway use.
Note – you cannot ride or drive on a UK motorway if you are on a provisional licence and need L plates to legally use the vehicle
I would watch this video showing the good and bad about motorways and low powered bikes
Depending on your tank it should be fine going from point A to point B. My bike was 90 something and it got me all around town. Filled it maybe once every 2-3 days but like a water bottle worth of gas. I freakin love those things! Btw you do need a drivers license to ride those I got pulled over many times.
I would watch this video showing the good and bad about motorways and low powered bikes