I recently entered a Norwegian port and was issued a fixed penalty notice for exceeding the cigarettes allowance, I therefore have to pay a fine of 400 kroner. I am now back in the UK and the fine has to be paid by Friday 26th of January. I have taken the giro slip to my bank but they do not understand it as it is all in Norwegian. Is there a way I can pay this fine quickly using my credit card, by phone for example?
Assuming that the payment is due to Statens Innkrevningssentral (the government collection agency), you can pay online with credit card by going the their web site, click on 'pay by card' and follow the instructions in the popup. They ask for a KID, which you will find on the bank giro slip you already have. Card payments are charged an additional NOK 40 fee.
Here some clarifications related to the comments on the question:
As long as the UK is a member of the EU and assuming that the OP is a UK citizen, he can't be refused entry to Norway because of an outstanding fine. There is no Schengen wide cooperation for fine collection, so this case can't be resolved in Calais and it is very unlikely that a failed payment will result in a SIS entry causing any issues for the OP trying to enter other Schengen countries.
What may happen if the fine is not paid is that:
The Norwegian authorities can 'forget' the claim. We are talking about a roughly 40€ fine and they can deem it not worth the effort to follow up on their claim.
They can forward the claim to a UK debt collection agency, which is likely to add substantial additional fees to the claim and at least annoy you for some time with letters and phone calls trying to persuade you to pay. The fine is not covered by any EU/EEA wide fine collection agreements and there are no bilateral agreements between Norway and the UK, so a UK agency will still probably (IANAL) have no legal right to enforce payment.
If not paid, the fine comes with a subsidiary penalty of one day imprisonment. If you fail to pay and you go back to Norway within the next 5 years (after which the claim lapses), the Norwegian authorities have the legal possibility to put you in jail.
Since we are talking about a very humane fine here according to Norwegian standards, I would not hesitate to pay it (about 45€ including payment fees) and resolve the issue. I mean the larger part of the penalty was likely that your cigarettes were confiscated by Norwegian customs and they had a 'street value' in Norway of at least a few hundred euros.