Baby freebies I have found and used:
Free Naty nappy becoming a Naty Ambassador:
http://www.naty.com/ambassador/
Free Mama Pack with £1 postage:
http://www.mamapack.co.uk/ The samples contained are eco friendly. If anything contained mentions a competition make sure you enter as they are little known brands so fewer people entering. I entered a comp advertised inside the lid of a sample of eco breast pads to win a Natracare maternity hamper - and won it
If you have a smartphone download the Boots app: Boots tailor voucher offers and freebies based on past purchases. I must have been on their radar for baby stuff from redeeming the Boots baby vouchers for their freebies as they gave me a voucher for a free pack of 80 disposable breast pads or a free MAM bottle. You can pre-load all the offers to your Boots Advantage Card so they will come off automatically at the till. Keep an eye on the app and pre-load anything relevant before you shop at Boots so you don't miss any offers.
Free Huggies:
https://www.pottytraining.co.uk/member/claim-a-free-sample/
Free Drynites:
https://www.drynites.co.uk/member/claim-a-free-sample/
Not *free* but don't forget to register with
http://www.caringeveryday.co.uk/offers-coupons - you can research online when your local supermarket has items with available vouchers on offer and print them for use then: maximising the discount you get off the products. You can get Johnsons Baby products for next to nothing doing this.
Register with
https://www.johnsonsbaby.co.uk/babyclub so you can redeem the codes from the backs of free packs of Johnsons Baby Wipes you get in Emma's Diary/Bounty packs: these can be used to get free baby items through their reward scheme. You can get boxes of Johnsons Baby wipes on offer that have codes and if you're stocking up (if you choose to use wipes you will be using them throughout potty training etc so no harm stocking up when they're on offer) you can easily amass enough points to get a reward. I have claimed three so far: they take a month to post them out so am waiting for them to arrive but it's worth doing if you're buying wipes anyway you may as well take advantage of the reward scheme

P.S. There is no joining bonus any more even though your schedule of transactions will mention one: they said they don't offer one any more.
I second Freecycle/Freegle etc groups: if you are happy planning ahead and have space to store items you can get almost if not everything you need for baby for free from these sites. Items given to me for free from these sites: moses basket, cotbed, baby clothes, cot mobile, baby bath, changing station, high chair etc you get the picture. Keep in mind: *loads* of people are having babies all the time and will want to get rid of baby stuff they no longer require when the time comes. If you are happy with secondhand these sites are brilliant. There are also freegive sites on social media connecting givers and seekers.
If you don't already have one: set up an Amazon wish list and add items you would like for baby to that. They have baby wish lists you can do separate to your own wish list if you like. You can give family and friends the link to the wish list/the name of the wish list so they can buy relevant gifts you *actually need* and you won't get any duplicates as once something has been purchased it is no longer visible on the list.
If you are having a home birth remind your midwife that they will need to supply the Bounty pack you would have been given after the birth in hospital. Bounty don't like to post them out but the midwife will be able to bring you one so you don't miss out.
I'll update more if I think of any more but keep an eye on
http://www.latestfreestuff.co.uk/free-baby-stuff/ which has an updated list of available items