It is accepted 'custom and practice' in many industries for suppliers that you have had contact with during the year to give gifts at Christmas. Unless there are specific terms in your contract concerning the receipt of such gifts, this is likely to be acceptable – provided that you act at all times in your employer's interests in your dealings with suppliers and aren’t influenced by gifts. However, to be on the safe side, it may be sensible to tell your manager about the gift, although this may depend on the nature and value of the gift.
Especially during difficult economic times, when some bad employers will seize on an opportunity to dismiss for misconduct, it is sensible to make sure you are familiar with your employer’s current policy on gifts, hospitality and so on, and to follow it to the letter.
Some gifts may be deemed by HM Revenue & Customs to be income, and would therefore be taxable.