You have two incompatible fittings.
The UK ceiling rose is standard - it is normally¹ the place where wiring is connected to and from other nearby lights (including those in other rooms). That is why there are more wires than you might expect.
In fact you have fewer wires than I would expect. Perhaps the light is the last one in a radial lighting circuit - so no onward cable. Perhaps there has also been some other non-standard or unusual wiring arrangement.
In any case you cannot assume that you simply connect together all wires of the same colour. When you replace a light, it is usually necessary to make a careful note of the existing connections and not disturb anything other than the two wires (plus earth where needed) to the light.
UK ceiling roses use the lamp cord to suspend the weight of the light. Strain relief is provided in the ceiling rose.
The Ikea lighting connector is of a type more prevalent in continental Europe. I believe it is designed to hang from a ceiling hook. It can probably support more weight.
You need to either
- Adapt the ceiling rose to take your Ikea connector
- Replace the ceiling rose with an accessible junction box
- Add a ceiling hook supported in a ceiling joist.
- Remove the Ikea connector
- Remove the white plastic part with the connectors labelled L and N from the black wires and discard it.
- Connect the two black wires from the light to the outermost connections on the ceiling rose.
- The black wire formerly connected to L for live (or "line" in modern terms) goes to the connection where the brown wires are in your picture.
- The other black wire formerly connected to N for neutral goes to the blue wires.
- However, for the black wires it doesn't actually matter which one goes where, assuming there is no on-off switch in the light itself. Switches always need to be in the live side.
I recommend the latter approach.
Typical wiring for UK light circuits
- The brown tape on blue wire indicates switched live (this blue wire is not neutral). Sometimes this tape falls off and gets lost.
- Grey cables are "twin and earth" (T&E)
- The cable between switch and rose should ideally be "twin brown and earth" with two brown wires. Most electricians just use the ordinary T&E and use tape to mark the blue wire.
- Some electricians swap the position in the rose of the brown and blue from the switch. When you see the blue connected to two browns you are expected to understand what the electrician did.
- Older homes will have T&E with red and black instead of brown and blue.
- Earth wires are bare copper. Green/Yellow striped sleeving must be added inside ceiling rose (or in other junction boxes etc)
- Ceiling rose contains all connectors needed.
- Last light on a circuit has fewer wires in the rose.
There are many variations on this.
¹ In some UK houses, perhaps mostly in houses built in the early to mid 20th century, wiring junctions were made not in ceiling roses but in separate junction boxes. In some cases, these junctions can occur in the back-boxes for switches. In these cases, the fixed wiring at ceiling roses should be simpler and might consist of only one set of neutral, switched-live and (in more recent installations) earth.
- Hat tip to AndyT for pointing this out.