Reality Check: What have rating agencies said about Brexit?

The question: P.M. asks BBC Radio 4's PM programme: "Have any of the credit rating agencies (eg Moody's), expressed a view on what effect a Brexit vote would have on our credit rating?"

Reality Check verdict: Standard and Poor's have said it would probably lower the UK's long-term credit rating. Fitch said it would review the UK's credit rating but did not now anticipate a downgrade in the immediate aftermath. Moody's said a vote to leave could lead to a negative outlook due to greater uncertainty and a weaker economy.

The UK government runs a deficit, meaning it spends more than it brings in in taxes. The government funds it by borrowing money.

As a country, we also have what is known as a current account deficit.

This is a deficit in the whole economy, not just the government's finances.

It is part of the balance of payments.

The UK's sovereign credit rating reflects how likely the government is to repay its debts.

There are three closely watched international credit rating agencies that assess this:

• Standard and Poor's

• Fitch

• Moody's

Standard and Poor's has said it would probably lower the UK's long-term credit rating in the event of a Brexit, describing a vote to leave as a "serious risk" to the economy, in particular financial services and exports.

It is the only agency that still rates the UK as AAA - the top rating.

Fitch said it would review the UK's sovereign credit rating in the event of a Brexit, adding that the short-term volatility and uncertainty it could cause and any delay in negotiating trade deals would both undermine the UK's AA+ rating (already one below top notch).

However, it did not anticipate a downgrade in the immediate aftermath of a vote to leave.

Moody's also rates the UK as one level below its top grade at AA1.

It said a vote to leave could mean a negative outlook as a result of the increased uncertainty and a weaker economy.

It matters because if the UK's credit rating was downgraded, borrowing would get more expensive, making the deficit more expensive.

Fitch believes the UK will vote to remain in the EU on 23 June, Standard and Poor's says it is a "close call", and Moody's has expressed no view.

Read more: The facts behind claims in the EU debate