Well... The £500m was due to the periodic security revamp and (probably planned) coincided with Britain EU departure. As we should all know there isn't and never was any requirement to have a burgundy coloured one.
BRITAIN'S iconic dark blue passports are set to make a return as part of a £ 500million post-Brexit redesign
The traditional blue British passport could make a return as part of a £500-million post-Brexit redesign
Last December, the then Immigration Minister estimated the cost to be £500 million
"In a tweet posted early on Sunday morning, the European Parliament’s UK office announced the “breaking” news that all EU passports would switch in colour to dark blue, mirroring the UK’s insistence that its documents will change colour after Brexit."
"But clicking on the link included in the tweet takes users to the original 1981 rules on passport design,"