There is always a way around creating additional space in your home.
You don't have to go all out and do a Kevin McCloud ‘Grand Design’ scheme.
A quick get out of jail card is to re design the internal layout of your existing footprint, it may just be the original design suited it's day however, peoples requirements these days are very different from the 70s, 80s and even the 90s.
Gone are the days when there was a sink in every bedroom, solid walls throughout making the alteration process unthinkable without structural supports, even more recently it was fashionable to have en-suites in all bedrooms has now reverted to the master bedroom with an en-suite (at a push) and generally accepting a family bathroom on the principal of sustainable living, after all if you are on a budget to renovate a house, four bathroom fit outs (supply, fit, tiling, sanitary ware, shower system) can be IRO £5-10K per room. That is unless you are partial to a Bangladesh latrine set up!
The obvious answer is to provide your house with an extension, and again, you don't have to be the person to reinvent the wheel. The reason basic designs work are because…. well, they work!
Currently, until 2016, the Government have relaxed the planning laws within the Permitted Development (PD) rights to extending your residential house, be it semi detached or detached. There are a number of things to take into consideration but if all boxes can be ticked then there will be no need to go through the planning process. Even if you do not meet the PD criteria for restricted size, there is the Neighbour Consultation Scheme which again avoids the full planning process. Best thing to do is check with your local authority, building designer / Architect or simply do the research yourself. Here is a link to get you to a site that can assist: www.planningportal.gov.uk/uploads/100806_PDforhouseholders_TechnicalGuidance.pdf