The financial sector is broadly pro-Remain. So this 'no deal' prospect is scaring them quite a bit.
What it means: The value of the pound has gone down to its lowest level in almost a year. In simple terms, currencies change in value because people buy or sell them, depending on how well they think a country is doing.
It's kind of like investing in a business - if you think a country's doing really well, and is likely to do better, you'll buy lots of their currency - which will make that currency worth more (because so many people want it, so the price goes up). But the opposite is also true: if you think the country's not doing so well, you sell off the currency, and its value drops.
The latter is happening to the UK: the pound is now worth $1.29, or €1.1. That's good news for people exporting British goods abroad, because they're now cheaper. It's bad news if you want to buy goods from abroad, or go on holiday, because you'll need more pounds to afford the same number of whatever currency you're using there.