I need to know if there's an easily accessible stain remover (I live
in London, UK) that will Very Effectively Remove any
Blu-tack/blue-tac/blu-tac stains I have right now on my wall, from
sticking up posters and photos, without harming the paint.
Preferably it would be something I could find around the house (i.e.
vinegar - helps to remove bubblegum from carpet). But if I must buy
something then I will - If it's not too expensive.  I urgently need an
answer as I am moving out of my rented flat in 3 days.

Hello Myri

According to the Blu-Tack website the best way to remove Blu-Tack
stains is to use a citrus-based stain remover but this will generally
only remove faint stains.  In my list of links at the end of this
answer I have provided some example products that may be of use (but
you may also have something in your cleaning cupboard that will work
just as well).  You should be able to find a suitable cleaning product
in your local supermarket or hardware store by looking at the
ingredients.  These types of cleaner usually list d-limonene as one of
the ingredients.

I have also included a list of links to recipes for homemade
citrus-based cleaners, which I would use at your own risk!

If the walls have been painted for some time and the posters been up
for a number of years, the oils in Blu-Tack are, according to the
official site, "sucked out" by the porous nature of the old paint.  If
this is the case the only solution that Blu-Tack.com provide is to
remove with sugar soap and repaint the area.

If you have any further queries on this subject please ask for
clarification and I will do my best to respond swiftly.  Good luck
with the move!

Useful Links:
http://www.blutack.com/help.htm
http://www.vikingtapes.co.uk/health8.htm
http://www.cleaningproducts-shop.co.uk/cgi/product.pl?c=www.cleaningproducts-shop.co.uk&category_id=1&
http://www.prochem.co.uk/CARPET.htm
http://www.ems.org/household_cleaners/alternatives.html#citrus

Citrus cleaner recipes:
http://www.recipezaar.com/r/q=citrus+cleaner
http://www.recipegoldmine.com/house/house341.html
http://www.recipegoldmine.com/house/house317.htm
http://www.stretcher.com/stories/99/991018l.cfm

I haven't used blue-tac, but I used a white version of it that left
gray stains.  They can sometimes be removed by erasing them with a
**very clean** pencil eraser.