Like the other sat-nav apps we've tested, Co-Pilot can be used in both portrait and landscape: the display will simply adjust depending on orientation.

The My Places area of the app enables you to store favourite destinations as well as your home and work addresses. You can also plan routes easily for future retrieval as well as work out the best route between multiple stop-off points.

Co-Pilot for iphone

Co-Pilot for iphone

One area that did disappoint was the walking directions. Much has been made of the poor performance of the GPS chip in the iPhone, but in-car this doesn't present too much of a problem - even if the display is a little slow to update after you've made the turn as instructed.

However, on foot this problem is clearly exposed and in our experience the app can only be used as a guide rather than a definite navigation tool when walking - it simply doesn't pick up your updated location quick enough - not even as quickly as the Maps app does.

Co-Pilot for iphone

This wasn't helped by the mapping itself - here we're being directed up a hill and back down again despite there being a clearly better route (the blue line is an 'as the crow flies' representation of where we need to walk).

Co-Pilot for iphone

Other now-standard sat-nav features, are the real Signpost display matching real-life signs and Lane Assist - pop-ups at the top of the display show which lane you need to be in. ClearTurn is designed to show key motorway junctions more clearly.

As a final note, and having spent some time using the iPhone as a sat nav, we'd definitely recommend you also invest in a cradle such as Belkin's TuneBase FM. Not only is it great for holding your phone in place, it means you can also hear the instructions through your car stereo and answer calls hands-free, too.

So is it worth the £26? Definitely. Co-Pilot is so far the best sat-nav app we've seen for the iPhone. If you've not already got a navigation app or a standalone device it's an absolute snip (though the in-built GPS chip is not the finest for walking or cycling). But, of course, the real question is whether the TomTom app is worth twice the cost. Check out our TomTom for iPhone hands-on review.

-------------------------------------------------------------------------------------------------------

Liked this? Then check out A week with the iPhone as a sat-nav

Sign up for TechRadar's free Weird Week in Tech newsletter
Get the oddest tech stories of the week, plus the most popular news and reviews delivered straight to your inbox. Sign up at http://www.techradar.com/register

Follow TechRadar on Twitter