7 or 8 years ago I was eligible to apply for British Citizenship having held the Indefinite Leave to Remain status for the required time period. At the time the cost was a few hundred pounds so I put it off. This year, I decided to finally get on with it. This meant studying and passing the Life in the UK Test, attending a (surprisingly emotional) Citizenship ceremony to swear allegiance to the Queen and get interrogated by someone at the passport office. I did these things in order to finally receive my British passport. All up it cost me around £1,000. The difference of £600-£700 is what you could call procrastination tax.
The passport office chap asked why I wanted a British passport and I'd replied 'Because the queues are shorter.' In hindsight I think I should have said something more ingratiating but it didn't matter because I received my passport a few days later.
(Photo above is from our first trip to Ibiza, in August - which was the last time I flew to Europe on my New Zealand passport. The light is natural and we loved it there, definitely going back.)