Here are some popular classified ad websites in the UK where you can post ads for free or a small fee, depending on the category and location:

1. goroo Classifieds

• Website: https://gorooclassifieds.com/
• Key Features: goroo Classifieds allows you to sell everything from furniture and electronics to vehicles and properties. It offers free ad with a wide reach across the UK.

2. Freeads

• Website: freeads.co.uk
• Key Features: Freeads is a popular site for buying and selling items locally. It’s free to post in most categories, with paid options available for premium placements. It covers a range of categories, including pets, motors, jobs, and properties.

3. Preloved

• Website: preloved.co.uk
• Key Features: A UK-based classified site that focuses on second-hand items. You can list most items for free, with options for upgraded listings. Preloved is popular for selling used furniture, clothing, and pets.

4. Vivastreet

• Website: vivastreet.co.uk
• Key Features: Offers free classified ads across a wide range of categories, including jobs, vehicles, properties, and services. Vivastreet has a significant user base in the UK and provides paid options for featured listings.

5. Friday-Ad

• Website: friday-ad.co.uk
• Key Features: A long-standing classified ad site in the UK that offers free and paid listings in various categories, such as cars, jobs, pets, and services. It’s popular in certain regions and has a print version in some areas.

6. UK Classifieds

• Website: ukclassifieds.co.uk

• Key Features: Free to post ads for a variety of categories, including real estate, vehicles, services, and general items. It offers upgraded ad options for more visibility.

7. Craigslist UK

• Website: craigslist.org/about/sites
• Key Features: Craigslist also operates in the UK, with different sub-sites for various cities. It offers free classified ads in a wide range of categories, but is less popular than some UK-specific platforms.

8. Loot

• Website: loot.com
• Key Features: Loot is a UK-based classified site offering free and premium listings in categories like property, motors, jobs, and services. It's a well-known name with a strong local presence.

9. Adzuna

• Website: adzuna.co.uk
• Key Features: Primarily a job search engine, Adzuna aggregates listings from various sites and allows employers to post job ads directly. It's great for recruiting or finding job opportunities in the UK.

10. Netmums Nearly New Board

• Website: netmums.com/nearly-new
• Key Features: A classified section on Netmums, a popular parenting site in the UK, where parents can sell or give away used baby and child items. It's free to use and targets a niche audience.

11. Shpock

• Website: shpock.com
• Key Features: A mobile-focused classified app known as "the boot sale app," Shpock allows users to buy and sell items locally. It’s user-friendly, popular for selling clothes, electronics, and household items.

12. Pets4Homes

• Website: pets4homes.co.uk
• Key Features: The UK's largest pet classifieds website, specializing in selling pets, pet services, and accessories. It’s a go-to platform for breeders and pet owners looking to rehome pets.

13. The Freecycle Network

• Website: freecycle.org
• Key Features: A global network with UK groups, Freecycle focuses on giving items away for free to keep them out of landfills. It’s ideal for people looking to declutter or find free items.

These platforms cover various needs, from selling general goods and pets to finding jobs or properties. Depending on what you're selling or advertising, you can choose the most suitable platform for your needs.