Been using Aldi £3 glasses with interchangeable lenses for years, but they scratch easily, this isn’t so much of a problem because I normally lose then before I can no longer see through them. Must have had at least 10 pairs over the last few years!
Anyway I’m down to my last pair.

Do what do you lot use?
Will be using them for night riding too, so need to have interchangeable lenses or photochromatic/transitions lenses, do these go clear enough to ride at night?
Anti scratch would be good too.
Budget is up to around £40.

If you knock your budget up a few quid, you could get a set of Bloc Shifter XR’s

They’re brilliant quality! Absolutely bombproof. They’ve 4 Lenses you can swap in a couple of seconds. The clear lenses are fine for night riding. They come with a nice case to keep your lenses in too. I had a pair for years, managed to lose them, so just brought myself another pair.

They don’t look too ‘bikey’ either, so you can wear them off the bike without looking like a complete spod!

I got some Tifosi for around that price. Quite happy with them

Bolle Contour safety glasses off ebay for ~£8 pr. They are CE approved anti fog, anti scratch, impact resistant etc…etc. far better quality than a lot of ‘premium’ named cycling glasses 10x the price!!

Ok not interchangable lenses but you can get clear, ESP and tinted lens versions.

I normally ride in the ESP ones in daylight as they have enough of a tint for sunlight and have a pair of clear in the backpack in case it gets dark.

Or if you want interchangable, Planet X are flogging off various glasses Incl photocromatics;-

http://www.planet-x-bikes.co.uk/c/q/cycling_glasses

the bolle siliums I have are anti-fog but fog up a lot

could do with some vents as they sit quite tight on my large tefal forehead

Another vote for Bolle Contours. Look great. Have every feature. Light weight. Anti mist is fantastic – £8.00. I’ve been using them for a good 3 years or so now. Jusy buy a new set at the start of every season. I’ve had expensive sets that have been shocking at keeping mud out of yuor eyes!

The Endura Spectrum glasses are great. I use a yellow set for everything, it’s fine at night and brightens up any overcast day into something much nicer… I mean it adds crucial contrast so I can shred with greater accuracy.

They seem to be about £14 most places, have antifog and both a hard and soft case. A wash every now and then restores the antifog and I’m not too precious about them. For the price you could get a clear and tinted set and have money left over.

I’ve got some Bolle safety specs, not sure which model, they scratched easily.
I’ll check out some of the other suggestions.

I have just bought some Tifosi masts. I paid £69 from a shop as I wanted to ensure they were genuine but can be had in the £45 region on the Bay.

Look great off the bike too and the photochromic lenses work really well with a good variance from light to dark.

Not me…..