The most common and most likely answer to this crossword clue is the 7 letter word MECCANO
M
E
C
C
A
N
O
More clues leading to the result MECCANO
- Miserly old city council imported construction kit
- Acme Co working to introduce new construction project
- Centre for enthusiasts addicted to revolutionary toy
- Tin with cobalt plating found on number one toy
- Construction set in holy city, on roundabout
- Kit is able to enter “Come Dancing”
- Can come to play with model construction set
- The first minor entering Chitra's cherry and nectarine orchard gets a toy set
- Model construction system can come apart
- It was used for building the holy city? Wrong
Buddy explains!

The straight part
We know that "Model construction system" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case model construction system = meccano.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.