Spotted that JD sports have a free delivery no min spend promo running until tomorrow, which is automatically applied at checkout. Here's a list of other retailers currently offering free delivery.

JD sports - free delivery until 4th May
https://www.jdsports.co.uk/

Dunelm - free delivery uisng code fedel14 (lots of low cost home items)
http://www.dunelm.com/

Holland & Barrett - use code WELCOME17 and can also combine with 20% code PUREGYM (thanks spasguidedogs) - lots of reduced clearance food
http://www.hollandandbarrett.com/shop/offers/reduced-to-clear/

Superdrug - Free delivery for Health & Beauty Card members, can signup free online instantly
http://www.superdrug.com/beautycard

Boohooman - 50% off and free delivery using code BLANDBYNAME50
http://www.boohooman.com/

Burton - Free express delivery using code MAYDEL (expires today)
http://www.burton.co.uk/

Clarks - Free delivery for a limited time
https://www.clarks.co.uk/

Debenhams - Free delivery on beauty items using code SHA5
http://www.debenhams.com/

H&M - 25% off one item and free delivery when you subscribe to newsletter
http://www2.hm.com/en_gb/customer-service/newsletter.htmln

Cotton Traders - Free delivery using code XCLA
http://www.cottontraders.com/

Boden - 20% off and free delivery using code A6H8
http://www.boden.co.uk/

Tesco Direct - Free one month delivery saver trial to get free delivery £10 min spend, useful on large furniture items as delivery can be extortionate
https://www.tesco.com/deliverysaver/

Works - Free delivery £10 spend using code QUIDEL10
https://www.theworks.co.uk/

Aldi - Free delivery on posters using code SPRING17
http://www.aldiphotos.co.uk/posters/

Clarins - Free delivery using code DEL16
http://www.clarins.co.uk/

House of Bath - Free delivery using code XQHL3
http://www.houseofbath.co.uk/

Boux Avenue - Free delivery applied at checkout for a limited time
http://www.bouxavenue.com/

Damart - Free delivery and 20% off using code 11379
https://www.damart.co.uk/home

Currys - Ongoing free next day delivery
http://www.currys.co.uk/gbuk/index.html

Zalando - Free delivery (thanks gooner)
https://www.zalando.co.uk

AO.com - ongoing free delivery
http://ao.com/

Music Magpie - ongoing free delivery
http://www.musicmagpie.co.uk/

Game - ongoing free delivery
http://www.game.co.uk/

Tredz - Free delivery (thanks gooner)
http://www.tredz.co.uk/delivery-info

Schuh - Free ongoing delivery (thanks nathan)
http://www.schuh.co.uk/

Oasis - Free delivery using code GOODTIMES (excludes sale)
http://www.oasis-stores.com/gb/home

the codes WELCOME17 and PUREGYM do not work together for me - its one or the other
- bayhabourbutcher