Hi - Sorry, I can't comment on the NI position, but the HSE have guidance on the subject which I've provided below if it helps (and I suspect the advice is likely to be broadly similar) so long as the vehicle is otherwise legal for road use.  Please also consider that there may also be driver restrictions.

HSE Guidance on Telehandlers on the Public Highway

Travelling with a tractor mounted fore-end loader or telescopic materials handler on the public highway: general guidance for safe operation

When travelling on the public highway, the forks (or other front-mounted handling attachment) should be:

• removed and carried elsewhere (e.g. on a trailer) or
• folded back and secured or
• covered/protected by an appropriate guard. 

If this advice is not followed, the attachment may be regarded as a dangerous projection, other road users may be deemed to be at risk, and the driver may be prosecuted for dangerous driving.  Keep the centre of gravity of the loader as low as possible to improve stability. Positioning the loader in the lowered position will also improve visibility and aid driver observation from the cab.  Driving, waiting to pull out from a gateway or field or manoeuvring with the loader raised and projecting beyond the machine could create a risk to other road users such as lorry drivers. 

Do not travel on the public highway with the machine attachment carrying a load, as this may contravene road traffic legislation.  Do not lift or lower the loader and turn at the same time as this can induce instability, particularly if carried out at speed.

Before driving on the public highway, you should also check the following:

• Select 2 wheel steer mode on multi-mode steering machines
• Independent brakes are latched together (if fitted)
• Differential lock is disconnected (if fitted)
• The machine is as clean as possible and will not deposit excessive mud/muck/stones on the road
• Indicators, windscreen wipers, and lights are in working order
• Mirrors are fitted, properly adjusted and clean
• Cab windows are clean
• Side shift is centralised
• Lap belt fitted and worn

The risks arising from machines turning out of fields or yards onto the public highway can be reduced by implementing suitable control measures.  For example:

• If the exit point is frequently used, install permanently fixed mirrors at a suitable vantage point to help the driver see on-coming traffic
• Use a banksman to monitor/control vehicle movements
• Display suitable warning signs to alert traffic
• Good hedge management can improve visibility on exit from fields
• Create wider access points/gateways to allow more space for turning and to facilitate waiting with the boom lowered.

For more information in relation to driving machines on the public highway contact VOSA or the police.