Being in a customs union with the EU the same as staying.
The idea of creating a special EU-UK custom union is gaining support. However, such customs unions generally work best for goods and the UK has a booming service industry. Negotiating a deal for the service industry is what will matter at the end. The EU wants to trade with the UK for multiple reasons. Mainly, European supply chains are so interlinked with the British market that finding new routes and sources will be too costly for businesses.
Some are troubled by the idea of a customs union because it could mean accepting what the EU says. They have reason to worry but many experts believe the UK could actually get a better customs union deal than other countries, like Turkey, for example.
The idea of any union with the EU is a big No! for Brexiters and one can’t blame them as their wish is for the UK to leave Brussels’ shadow as soon and as rapidly as possible. And if they don’t like the custom union they wouldn’t fall in love with its so called 2.0 version which adds membership to the EU single market. However, the UK will most likely be asked to keep its borders open for EU nationals wishing to work in Britain.
What all of that means is that Brexit could end up being just a signed paper between London and Brussels.
One could wonder if this is what Brexit mean, wouldn’t it be better to just stay in the EU? From an economic point of view it is. From a political… well, politicians are desperate to deliver Brexit even if it means staying in the EU but not exactly.