Dulux also do a product called 'brushwood', you can get it in different finishes, oak, teak, beech etc.
It comes in two parts, the first part is waterbased, and gives you your base, if your going from dark to light then you would need 2 coats of this.
The second part is your coloured varnish, the down side with is that the varnish is quite glossy, but if that suits you then okay.
I have used this over existing white paint for the client, as they wanted thier staircase to tie in with their stained woodwork in thier lounge.
I must admit, it went very well, and its difficult to see which is the real stain and which is the pretend one.
If its done right, it can look quite nice, but I dont like the glossy finish, but you can then sand the gloss coat back a bit, and apply an ordinary satin varnish to dull it down, again I did this on another job, and it took very well.
You can buy paint and grain, and brushwood from 'Homebase', I got some about 2 months ago, (brushwood) I saw only the paint and grain in B&Q the other day.
So it is out there.