How much are you willing to spend?
Give me a figure and I'll take you from there :)
Personally I wouldn't touch Argos with a barge pole for a keyboard, sorry Pleb. They charge way more than lots of dedicated music shops for very cheap and basic stuff, on the whole. OP, let me know what you want to spend and I will recommend what and a selection of where (and I have no vested interest in anywhere, I'm just a keyboard and piano teacher).
that you were recommended a discontinued keyboard, btw. Not that the one you've been recommended is bad, far from it; quite a few of my pupils have had this model in the last few years and it's fitted the bill very nicely. Just that a good teacher should be keeping their eye on the ball of new developments as the technology moves so quickly in this game and models are discontinued on a fairly frequent basis as new technology overtakes. You don't want to be buying into old technology - unless you can pick one up for £50 on ebay and then I'd say it would be worth it.
The main features you need are -
Full sized keys. At least 5 octaves - 61 keys. This will suffice but 6 octaves - 76 keys - is better, though you lose out in terms of portablilty.
Good quality sound. Try a few out on piano sound. You will notice some sound much better and more authentic than others, Generally, the newer the model, the better the sound. Yamaha and Roland both have good sounds generally. Don't touch Casio - cheap rubbish for kids to mess around on. Play one and compare the sound to a Yamaha and you'll see what I mean.
Touch sensitive. You'll need to spend probably over £150 to get this if you're buying new, but you may as well not bother without. A keyboard with no touch sensitivity will barely get you to Grade 1.
At least 32 note polyphony.
And if you can run to it, the ability to record to the keyboard and a registration memory. Once, again. though it's not essential at first you'll find yourself needing to upgrade very quickly without this.
If you give me a price bracket I can talk about more specific models. Hope this helps!