The only reasonable solution is going to hurt.
First time buyers are having a hard time obtaining mortgages and also a lot of flats (don't know how old yours is) have been sold at way over market value by the developers for a good 5 or 6 years since BTL became the latest "herd instinct" to follow.
Unfortunately the valuers instructed by mortgage lenders agreed with these high prices and loans were granted far too easily.
As mentioned I don't know if this happened in your case but Flat prices had increased by a bigger percentage than 3 or 4 bed houses during the boom period and now are declining also at a faster rate.
If you have had no viewings it may be down to price or FTB's not getting a mortgage approved (3 out of 4 are being turned down) or simply buyers are waiting for the next wave of declines in property prices.
I wanted to get out of property at end of 2007 and early 2008 and even then discounted the asking prices of my BTL properties by 5% from the norm. Maybe if you are really desperate to sell at this particular time you will have to make your flat more attractively priced to the buyers that are left. Sorry, this is a hard fact of life but Supply and Demand drive prices.