The FTSE 100 has opened 0.36% lower at 6,838.25.
The FTSE 250 is 0.34% lower at 18,424.09.
Meanwhile, the pound is down against the dollar so for this morning - off 0.18% at $1.2858.
It is marginally off against the euro at €1.1295.
A quick update on sterling as the US markets open.
Against the dollar, the pound is now off the day's highs but still in positive territory - up 0.05% at $1.2867.
The pound is rising against the dollar, up 0.2% at $1.2882, as the London markets open.
Against the euro the pound is up around the same amount at €1.1299 - its highest level against the single currency since November.
More on sterling ahead of tonight's vote.
The pound is down around 0.3% at $1.2830.
MUFG strategist Lee Hardman told Reuters: "It's a done deal that the vote will be defeated. Initial market focus will be on the scale of the defeat and the expectation is it will be heavy -- 100-200 votes
"The surprise will be if the defeat is narrower. The balance of risks (for sterling) is to the upside as people expect a big margin... But it will still leave us in a state of deadlock".
Just a reminder of where the pound has been trading against the dollar over the last few years.
Before the Brexit referendum in June 2016 it was trading at almost $1.50.
It fell as low as $1.20 in early 2016.
Today it is trading at $1.2860.
The euro has slipped against the dollar after that data showing the weakest growth in Germany for five years.
It is trading at around $1.1458.
ING's economists tweet
It's a crunch week for Brexit, with a vote on Theresa May's plan for exiting the EU taking place on Tuesday.
The pound has slipped slightly against the dollar as the market opens, as the chart shows.
The dollar is trading 0.17% lower on the pound on Monday following comments by US Federal Reserve chairman Jerome Powell indicated that the central bank could pause interest rate rises.
Michael McCarthy, chief markets strategist at CMC Markets, said: "The market certainly liked what Powell said on Friday and the reaction has been negative for the dollar."
Lee Hardman, an FX strategist at MUFG, said: "Growing expectations that the Fed will pause on its rate hike cycle is weighing on the dollar and that will be a big factor in the coming days."
Meanwhile, Philip Wee, currency strategist at DBS, said: "Last Friday's strong US jobs data suggested that recession fears were overblown."
Although it rose following positive December jobs growth data, the US dollar has slipped against the pound on comments made by Federal Reserve Chairman Jerome Powell.
The US dollar is now down 0.75% against the sterling at £0.7854.
The US dollar has fallen 0.06% against the euro at €0.8772.