The most common and most likely answer to this crossword clue is the 11 letter word PLANTAGENET
I've seen this crossword clue in The Guardian
P
L
A
N
T
A
G
E
N
E
T
More clues leading to the result PLANTAGENET
- Devise principle inspiring a key royal dynasty
- House key carried by factory representative
- Place spy outside English royal house
- Hide a catlike animal in house
- Factory representative seen round back of terrace house
- Put spy in place to ensnare English royal family
- Place and time to bag an old house
- Mole with information given during meal about royal dynasty
- Scheme, what’s believed to allow accommodation of silver in royal house
- Works with a man to house European leader
Buddy explains!
The straight part
We know that "old house" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old house = plantagenet.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.