Analysts upgraded their Carphone Warehouse forecasts after a powerful first-half performance from US venture Best Buy Mobile.

In the UK, however, losses are rising at the fledgling Best Buy electricals big-box business, which launched here in the spring.

Carphone reported that Best Buy Mobile US generated a profit share at the interim stage of £43m and upped full-year guidance from £55m to as much as £95m.

But the Best Buy UK electricals stores suffered a loss of £29m and in the full year that is likely to rise to between £50m and £55m - original guidance was £10m lower.

Carphone Warehouse chief executive Roger Taylor was sanguine about the big boxes’ performance. He said: “Customer response to our first five Best Buy-branded big box stores has been overwhelmingly positive.” The launch last week - a day before Carphone’s results - of a Best Buy transactional website meant “Best Buy gains national reach and is able to compete as a truly multichannel retailer” Taylor claimed.

Oriel analyst Ben Hunt said: “Following the raised guidance we have upgraded our numbers significantly. Each of the three businesses within best Buy Europe offer good potential growth stories.”

UBS analyst Andy Hughes said: “Big box loss guidance has increased and we assume a similar rate of start-up losses in 2011/12. Beyond this we would expect the loss to decline either from covering central overhead with more openings or from refining the concept.”