Ebay are selling them with fairly quick delivery but standard price seems to be about £1 each

Valves are good

Screwfix has a range

Good luck finding a tested mask available online that hasn’t had its price inflated or you have to buy a bulk order of tested masks at £30 each. Found this on a retailer’s website:

Which mask is best for Coronavirus? We recommend the following Masks, FFP1 GOOD (filters 80% particles), FFP2 (N95) EXCELLENT (filters 94% of particles) FFP3 (N99) THE BEST (filters 99% of particles). Surgical Paper Face Masks, Basic Dust Masks offer very little protection! (filers just 4% of particles!) you must buy a mask with a FFP rating

You won’t find any of these but it’s worth a read.

[Link]

‘T-shirts, bandanas and even sanitary towels: Homemade face masks may offer protection, too

Many people are opting to make masks at home using cloth or other materials - some have even been pictured using sanitary towels.

The Centers for Disease Control and Prevention (CDC) in the US recommends people use cloth face coverings when they go out in public and even has a how-to guide for people to make their own out of t-shirts or bandanas.

The intention of these is not specifically to protect people from catching the virus but to prevent the spread of it by encouraging such widespread use that people who are infected but don't know about it wear something that blocks the viruses being expelled on their breath.

However, European researchers have suggested these may not be effective and up to 90 per cent of particles can make their way through the fabric.

The European Centre for Disease Prevention and Control said rates of illness were much higher among healthcare staff using masks made out of cloth instead of surgical masks.

It said: 'Altogether, common fabric cloth masks are not considered protective against respiratory viruses and their use should not be encouraged.’

‘ 'In the context of severe personal protective equipment (PPE) shortages, and only if surgical masks or respirators are not available, homemade cloth masks (e.g. scarves) are proposed as a last-resort interim solution by the US CDC until availability of standard PPE is restored.'

Edited by Rudi Hedman (21 Apr 2020 3.16pm)

COYP

I've wondered about making some cloth ones using a double layer of garden fleece between the fabric. This should increase the density, but not too sure how well I'd be able to breathe through it....

A stairway to Heaven and a Highway to Hell give some indication of expected traffic numbers