We run a dehumidifier in our flat for about 1/3 of the time over the winter. That costs us about £50 or so in electricity[1], plus any spare heat it outputs is not wasted as that just means the heating needs to do less work.
Living in a house converted into flats means the ventilation is nowhere near good enough. Such flats weren't designed to have clothes dried inside and the ventilation routes that would have been present in the original house all get blocked up as the place is partitioned up. Even without clothes drying inside the flat we often get condensation on the windows just from the 3 of us that live here.
If we ever get our place refurbished (new wiring -> replastering -> redecoration) I'll get the builders to sort out the ventilation so the place can breathe better.
From an environmental stand point, I'd say not a good idea.
If the alternative is heating/drying a whole house to the point that clothes dry properly in it then a drier may be the more environmentally option. Of course, insulating and improving air-flow is the real correct answer, but that might be £000's rather than £00's.
Personally I'd just go for a dehumidifier next to an airer full of damp clothes just because it can kill two birds with one stone as we need a dehumidifier anyway (I can't run a tumble drier to remove damp from my flat).
Tumble driers are a huge cause of house fires too.
1. UK rule of thumb is 1W for an entire year costs roughly £1. So a 400W dehumidifier on for 8 hours a day for 5 months a year =~ £55.