IMHO.....here are some factors and suggestions you may wish to consider:
1) my apartment has windows on opposing walls which provides a decent air flow.....if your flat only has windows on one wall it will restrict proper air flow and will likely stink up the building common hallways.
2) I'm about a 100 yards from the ocean, as such I typically have a breeze coming off the ocean to circulate my indoor air....so you have to consider your typical outdoor air flows.
3) my apartment is long and narrow, as such the hallway door is a fair ways away from the living room where I grow the plants, thus the smell seldom travels near the doorway...... if your hallway door is close to your grow area, then this could be a concern.
4) you can position fans in your windowsill to push the air outside your flat, but you have to consider if that air exhaust will flow into someones flat
5) here in Canada it is legal to grow 4 plants, thus I have no risk of getting busted, maybe only a complaint from other residents, which I have never had....you should consider your British laws and how vigilant your local police are towards MJ
6) yes, there are times my living room reeks of MJ, especially when the sun is shining directly on them but personally I like the smell
Question....do you smoke joints in your flat?
if yes and have no complaints from the neighbours, then you should be okay with an indoor windowsill grow
cheers
ISK