Do not understand why MariaDB rejected REGEXP with 42000 You have an error in your SQL syntax

When I issue the following prepared statement:

SELECT COUNT(*) FROM MethodistBaptisms WHERE LOCATE(:district1, `district`) > 0 AND `area` REGEXP :area1

with the following parameters:

Array ( 'district1' => 'Oxford & Middlesex', 'area1' => 'Nissouri Twp.E&W')

I get:

Array ( [0] => 42000 [1] => 1064 [2] => You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'REGEXP 'Nissouri Twp.E&W'' at line 1 )

However if I manually perform the insertions and issue the query:

SELECT COUNT(*) FROM MethodistBaptisms WHERE LOCATE('Oxford & Middlesex', `district`) > 0 AND `area` REGEXP 'Nissouri Twp.E&W'

it works. If I change the query to:

SELECT COUNT(*) FROM MethodistBaptisms WHERE district=:district1 AND `area` = :area1

with the same parameters, it also works. So there is something specific to the REGEXP which I do not understand. I also note that I am not receiving the form of the error message that I would get if there was an error in the regular expression.

I have tested this against MariaDB 10.3.20-MariaDB-0ubuntu0.19.10.1 and MySQL 5.7.28-0ubuntu0.18.04.4 and I get the same resu