When you buy a house, there are lots of things that you will need to get in order before you start going out to view properties. Something that the UK is clamping down hard on is money laundering within the property market, so new laws now state that you need to have an AML ID check like this www.w2globaldata.com/regulatory-compliance-solutions-and-software/aml-id-checks when you buy a property in the UK.
When you first start to go looking around properties, it is likely that the estate agent will ask you for proof of funds. As well as being an important part of the check that you are not a money launderer, this is also due to the fact that the estate agent will want to make sure that you are in a position to be able to buy the property if you want to put an offer in.
You will need to have the funds ready, whether this is in savings, or via a mortgage agreement. Getting this ready beforehand is essential to the process.
You will also need to have a check done on where your funds are coming from. It is all well and good having the money, but you will need to provide the proof of where it came from. This is another measure that is taken to prevent money laundering. If the money is a gift to you for example (often from parents keen to help kids get on the property ladder!) then you will need them to confirm this in writing.