painting over grafiti

[Thunderchild]

our house has had black felt tip pen drawring done on the wall how can we paint over them with white or are we expecting too much ?

[Clanad]

I've used this product many times on several different stained areas... works very well... should be available in the U.K.
http://www.kilz.com/pages/default.aspx?NavID=6 1

[bookermel]

Marker is likly to 'bleed' through water based paints such as acrylics, emulsions etc. so you will need to create a barrier by usingin one of the following methods. A stain block like clanad has posted. You can also use an oil based undercoat or a shallac based primer such as BIN primer. I find BIN works for most jobs and because it forms a very thin layer it is easy to paint over.
http://www.zinsser.com/product_detail.asp?Prod uctID=10

[twiztwiz]

Well I know on a radiator I've removed permanent marker writing with simple nail varnish remover. Couldn't you try either white spirits or varnish remover on the wall or lightly sand it off?