Is there a way of adding Nectar points if I forgot to put in card details at the time of purchase?

Did you keep the recipt of the purchuse?

It's from play.com and hasn't arrived yet.

You should get a recipt with your order that has the amount of points you would have got, you might only be able to put the points on at a game shop as thats where you got them
take your recipt in and ask if they will put the points on your card
this usually works for most shops

it is an online store

Have you tried calling the Nectar Helpline? 0870 4100100 If you log on to [url]www.saynoto0870.com[/url] and put in that number it does give you an alternative. I've yet to work out how to put screen shots onto the website, and I can't be bothered to save as a picture and upload that, so the gist is below:

Nectar Points 0870 4100100 = 0844 8110811 020 72096355 Helpline
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Also ask for the Treatme support line (0845 2232970)

Or perhaps hunt around the site [url]www.nectar.com[/url] for contact us bit?