British households will be saddled with a tax-like financial burden for years if they vote to leave the EU, one of the world’s leading forecasting groups has warned.

The Organisation for Economic Co-operation and Development (OECD) said the average UK worker would lose out on a month’s pay by 2020, with further losses in subsequent years, if Brexit goes ahead.

Ángel Gurría, the OECD’s general secretary, told BBC Radio 4’s Today programme: “Brexit is like a tax, equivalent to missing out on about one month’s income within four years, but then it carries on to 2023, 2030.

“There is a consistent loss … That tax is going to be continued to be paid by Britons over time. What they would have had in their pocket to spend, they would not have. Therefore it is as real as tax.”

The OECD has calculated that lower economic growth will weigh on household finances. Details of its forecasts and how it made its calculations will be published at 10.30am GMT+1.

Putting himself firmly in the remain camp, Gurría added: “Why are we spending so much time, so much effort, and so much talent, in trying to find ways to compensate for a bad decision when you don’t necessarily have to take the bad decision?”

He rejected the idea, put forward by Vote Leave camp leaders, including the London mayor, Boris Johnson, that Britain would be better off in the long term outside the EU.

Gurría said there was no reason why the Brexit camp should assume the UK would be able to negotiate a better deal on trade, investment and migration outside the EU. “[There is] no kind of deal that would go better by yourself than in the company of Europeans.”