Lumia 520 is doing very well in UK as well, it seems. At Carphonewarehouse, UK where it is available at a monthly deal of £7, it is listed in the “Bestselling pay monthly deals“. The retailer has some of the best deals available for Lumia 520 in UK.
Also at operator O2 in UK, Lumia 520 seems to be “out of stock” currently. Both colors are sold out and the page mentions up to 14 days for delivery of the Lumia 520.
Thanks Pet3 for the Tip. Cheers!!