Is it practical / feasible to extend a house built in the 1860s, which has already had one extension ?

yes it is feasible it requires a lot of thought at the planning stage to keep it in character but this can be acheived with a good architect and an experienced builder who has worked on old buildings as there are generally no proper foundations so underpinning will be required also extension work to this type of property is more expensive because of the time for the work and the materials are more expensive but it can certainly enhance the property if carried out correctly i hope this helps

It is both practical and feasible to extend any home of any age. You may want to extend sympathetically with your existing building, the extent to which you are compelled to do this will depend on whether the existing building is listed or not. As to underpinning being required will depend on whether or not you intend to build on top of an existing structure, this would be decided by a structural engineer. Modern building practices such as insulation and wiring would have to be adhered to, your local authority on building control would be in a position to advise you on these matters.

I can only reiterate what is said above. It would not be a bad idea to see a few design & build companies and also see if you can see past works they have completed for clients etc. Whichever way you go it will be expensive, but will enhance and benefit the property.

It is very much dependent on several factors. Firstly What is the current state of planning i.e. was the previous extension erected under permitted development rights or with the benefit of full planning permission and if permission was sought and granted were there any onerous conditions attached. Secondly what is the relationship in size between the plot size and the existing building and thirdly although not finally is the intension to improve the family living space only or do you need to consider the commercial implications of the build i.e. by building the extension will you price your property out of the local market?