The exchange rate is hovering around €1.127, down from €1.128 earlier this morning.
Sterling’s strong performance at the start of the week has been quelled amid political speculation.
Boris Johnson further fuelled the Brexit debate with an article he wrote in the Daily Telegraph at the weekend.
Speaking on Brexit, Mr Johnson wrote: “Once we have settled our accounts, we will take back control of roughly £350 million a week.
Pound euro exchange rate: Sterling is struggling ahead of a speech on Brexit from Theresa May
“It would be a fine thing, as many of us have pointed out, if a lot of that money went on the NHS, provided we use that cash injection to modernise and make the most of new technology.”
He was reviving an earlier claim he made prior to the Brexit vote, and yesterday was both supported and criticised for doing so.
Prime Minister Theresa May is due to fly to Florence this week to discuss her vision for a post-Brexit Britain and the future ties with Europe.
British officials said it is likely that Mrs May has already told her cabinet of the details of her Florence speech.
Pound euro exchange rate: Sterling is buying €1.127
The looming Brexit update has prompted speculation Boris Johnson may quit if it does not go the way he wants.
But Mr Johnson has vehemently denied these claims. He told the Guardian: “I am mystified by all this stuff. Not me, guv. I don’t know where it is coming from, honestly.
“It feels to me like an attempt to keep the great snore-athon story about my article running. I think that is what is going on.”
The pound to euro exchange rate has stumbled due to the political uncertainty, according to experts.
Pound euro exchange rate: Sterling remains volatile to political events
GBP/EUR had a bumpy ride… market jitters over Theresa May’s Friday speech remain
Rewan Tremethick, currency analyst at TorFX, said: “GBP/EUR had a bumpy ride yesterday. Technical factors caused the pound to slump midday, although even without an unexpected drop GBP would have ended the day lower.
“Market jitters over Theresa May’s Friday speech remain, especially now rumours have surfaced Boris Johnson may quit the front bench if the negotiations don’t turn out the way he wants.
“GBP/EUR has now lost over a cent after hitting a two-month high on Friday.”
UK retail sales due out today could further influence the movement of the pound against the euro.