I've just paid 20% VAT and 6% Import Duty (26% in total) on the current value of the bike.
This is the definitive position:
VAT is usually payable to HMRC (Customs) if a vehicle is imported from outside the EU. If you are a VAT registered business then HMRC needs to be notified using the
NOVA (Notification of Vehicle Arrivals) system.
There are some exemptions to the payment of VAT on vehicles imported from outside of the EU. You would be exempt if you qualify for transfer of residence relief. You can qualify if you can prove the following:
- you are moving your normal home to the UK
- your normal home was outside the EU for a continuous period of at least 12 months
- you have owned and used the vehicle for at least 6 months outside of the EU
- you did not get the vehicle under a duty or tax-free scheme
- you are going to keep the vehicle for personal use for at least twelve months.
Furthermore, you may not pay VAT on an imported vehicle if it has been previously exported from the EU or the vehicle is imported from outside the EU and is registered to a non-EU resident.
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AND I haven't finished paying yet! In addition to the import agent's fee (that is, if you employ a specialist agency), I still have to pay:
First registration fee to the DVLA .................... £55
Cost of getting a UK reg plate made-up ........... £??
Change speedo reading from kms to miles ...... £20
MOT test .................................................. .. £30
Vehicle road tax to the DVLA ..........................£82
There may be one other fee of £85, which will is the cost of a
MSVA (Motorcycle Single Vehicle Approval) test, IF I cannot get hold of a COC (Certificate of Conformity) from the maufacturer's national agent from where the bike was first registered, which in my case is
Blue Wing Honda Ltd in New Zealand.

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I guess it could have been worse, as you are obliged to notify HMRC within 14 days of bringing a vehicle into the UK permanently. If you don't then you can be fined £5 for every day you’re late telling HMRC.
I imported my bike - ferry to Plymouth from Santander, Spain - on the 21st October last year (2015), but didn't notify HMRC until 23rd March this year. Therefore I could have been facing a fine of £700 (140 days x £5).
BUT no fine has been imposed.