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Not sash - they're pivot windows. From the 1970s, probably. Not perfect, but new sashes are around £5k for this bay, so I'd rather repair if possible. I;ve tried a few window specialists but no dice so far - maybe I just need to persist!
As @Airhead says, it's not great for access as it's 1st floor. However there is a front yard below, so scaffolding or an access tower could be used. If I were to DIY something I'd certainly go for a tower rather than a ladder.
I'd have thought it would be lousy with window specialists up there? Even though they aren't sash (or are thy - I can't tell), it may be worth talking to a sash repair specialist, as they do wood well.
Re-doing burnt sand mastic is a piece of piss though, so at least that bit is well within DIY territory.