I know this is over a week old now but I hope nobody minds me indulging in bumping it - I find church seating fascinating! They might seem a bit mundane but actually they are a microcosm of the prevailing churchmanship and ongoing changes.
The quintessential Victorian gothic church with rows of pews is really a reaction against Georgian churchmanship - private, high, walled pews; plain buildings; non-east facing in some areas (so not at all the tradition we are used to today) - and against falling attendance numbers. The design of those churches largely started with the Oxford Movement who believed, in extreme summary, that something had gone wrong with the church and that buildings mattered and should have symbolism.
Interestingly the furor over gothic rebuildings, that we now accept as normal church architecture, was possibly worse than current complaints over seating - they had satirical newspaper cartoons and fistfights in some parishes!
At the same time there was a 'build and they shall come' attitude to reversing low attendance numbers. Parishes were granted money basically to stuff as much seating in as they could (within set bounds of comfortable seat depth and leg space) and they had to guarantee that a certain number would be 'free' ie: not assigned to a family, and the seat backs had to not obstruct views. In some places churches were so crammed that pew removal started within decades (so it is not just a modern phenomenon).
Pews are never going to be removed from all churches in England - some communities won't consider it, some are too historically significant, some have survived without many removals so are deemed to contribute too much to the aesthetics and original design of the pace to remove, some are individually designed pieces of art that echo other elements of the building design. However, for many churches today the simple truth is that if the space is not made flexible (for different forms of worship and/or community use) the church will become impossible to run and the building will be at genuine risk of deconsecration and , if it is not taken on by a charity, will be sold and all its furniture stripped out.
Pew removal today is not done at a whim. Some money may come from sale of pews but it will be spent on chairs. Parishes will usually be encouraged to try partial removal or conversion to moveable pews before total removal. They will have to draw up plans, justify them, get approval from the diocesan advisory committee, the Victorian Society, and (if its 2* listed or above) from Historic England. The plans have to be displayed for a month and notice posted around the church - any member of the public can then write and complain to the chancellor of the diocese (who gives permission for the works) and he can decide to hold a court hearing if there is not agreement and/or lots of local complaints. It can take years to make the change and emotionally drain the volunteer members of the PCC!
And, while the early medieval church may not have had pews, there are some nice late medieval pews (15th century mainly) around if you look carefully - generally in small churches in rural areas that haven't had many alterations over the centuries. Most were taken out by the Georgians to be replaced by the box pews that the Victorians took out to replace with the pews that parishes are taking out today to replace with chairs and benches...
Anyway, I will stop being a geek over pews now!