Exhibit 31.2

CERTIFICATION UNDER EXCHANGE ACT
RULE 13A-15ANDSECTION 302 OF THE
SARBANES-OXLEY ACT OF 2002

I, Gayle Marshall Johnson, Chief
Financial Officer, certify that:

1. I have reviewed this annual
report on Form 10-K of Potomac Bancshares, Inc.;

2. Based on my knowledge, this
report does not contain any untrue statement of a material fact or omit to state
a material fact necessary to make the statements made, in light of the
circumstances under which such statements were made, not misleading with respect
to the period covered by this annual report;

3. Based on my knowledge, the
financial statements, and other financial information included in this report,
fairly present in all material respects the financial condition, results of
operations and cash flows of the registrant as of, and for, the periods
presented in this report;

4. The registrants other certifying
officer and I are responsible for establishing and maintaining disclosure
controls and procedures (as defined in Exchange Act Rules 13a-15(e) and
15d-15(e)) and internal control over financial reporting as defined in Exchange
Act Rules 13(d)-15(f) and 15a-15(f) for the registrant and have:

a)Designed such disclosure controls and procedures, or caused such
disclosure controls and procedures to be designed under our supervision, to
ensure that material information relating to the registrant, including its
consolidated subsidiaries, is made known to us by others within those entities,
particularly during the period in which this report is being
prepared;

b) Designed such internal control over financial reporting or
cause such internal control over financial reporting to be designed under our
supervision, to provide reasonable assurance regarding the reliability of
financial reporting and the preparation of financial statements for internal
purposes in accordance with generally accepted accounting principles;

c) Evaluated the effectiveness of
the registrants disclosure controls and procedures and presented in this report
our conclusions about the effectiveness of the disclosure controls and
procedures as of the end of the period covered by this report based on such
evaluation; and

d) Disclosed in this report any
change in the registrants internal control over financial reporting that
occurred during the registrants most recent fiscal quarter (the registrants
fourth fiscal quarter in the case of an annual report) that has materially
affected, or is reasonably likely to materially affect, the registrants
internal control over financial reporting; and

5. The registrants other certifying
officer and I have disclosed, based on our most recent evaluation of internal
control over financial reporting, to the registrants auditors and the audit
committee of registrants board of directors (or persons performing the
equivalent functions):

a) All significant deficiencies and
material weaknesses in the design or operation of internal control over
financial reporting which are reasonably likely to adversely affect the
registrants ability to record, process, summarize and report financial
information; and

b) Any fraud, whether or not
material, that involves management or other employees who have a significant
role in the registrants internal control over financial reporting.

|Date | March 31, 2009 |                                                 |  | /s/ Gayle Marshall Johnson | 
|---- | -------------- | ----------------------------------------------- |  | -------------------------- | 
|     |                | Gayle Marshall Johnson, Chief Financial Officer

A signed original of this written
statement required by Section 302 of the Sarbanes-Oxley Act of 2002 has been
provided to Potomac Bancshares, Inc. and will be retained and furnished to the
Securities and Exchange Commission or its staff upon request.

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