Here's a list of some of the leading national suppliers of plug sealing caps in the United Kingdom:

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Leading Suppliers of Plug Sealing Caps in the UK

1. Berry Global, Inc.

   • A major manufacturer known for its wide range of packaging solutions, including sealing caps.

2. AptarGroup, Inc.

   • Specializes in dispensing and sealing solutions for various applications, including pharmaceuticals and consumer products.

3. CML Innovation, Inc.

   • Provides innovative packaging solutions, including plug sealing caps for different industries.

4. O.Berk Company

   • Suppliers of packaging products including plastic and glass containers with various closure options.

5. Caplugs

   • Offers a variety of protective, sealing and cushioning products, including plug sealing caps.

6. Silgan Closures

   • Known for making closures for food and beverage industries, including plug sealing options.

7. Alcoa (now Arconic)

   • While primarily known for its metal products, it also provides closures and packaging solutions.

8. Container and Packaging Supply (CPS)

   • A supplier of a variety of packaging solutions including closures and caps.

9. Alpha Packaging

   • Offers a variety of bottle and jar closures, including plug sealing caps for pharmaceutical uses.

10. Pratt Industries

    • Provides sustainable packaging solutions, including closures for various applications. ```

This list includes companies that are known for their seal cap products, but it's always a good idea to verify their current offerings and market position, as dynamics in supplier capabilities can change over time.