We are just having replacement casement windows fitted into our 1900 house having researched the market thoroughly, or so I feel !
We found a company who offered to fit External Georgian Bar windows into the existing wooden frames of our house which meant that all the beautiful details above and below the actual window remain, both inside and out.

We currently have 5 out of 15 windows fitted (More going in today!!) and we are so pleased with them. We were really worried about taking any character away from what were beautiful feature windows and this just hasn't happened.

We are in the Gatwick area, and the company is http://www.teamframestrade.co.uk although their website does them no credit !

I hope that helps....